Copy the n-largest files from a certain directory to the current one. What are the advantages of running a power tool on 240 V vs 120 V? Dereferencing a null pointer always results in undefined behavior and can cause crashes. That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. ), NPD.CHECK.CALL.MIGHTNPD.CHECK.CALL.MUSTNPD.CHECK.MIGHTNPD.CHECK.MUSTNPD.CONST.CALLNPD.CONST.DEREFNPD.FUNC.CALL.MIGHTNPD.FUNC.CALL.MUSTNPD.FUNC.MIGHTNPD.FUNC.MUSTNPD.GEN.CALL.MIGHTNPD.GEN.CALL.MUSTNPD.GEN.MIGHTNPD.GEN.MUSTRNPD.CALLRNPD.DEREF, 45 D, 123 D, 128 D, 129 D, 130 D, 131 D, 652 S, Checks for use of null pointers (rule partially covered). This compliant solution ensures that the pointer returned by png_malloc() is not null. The n=0 is a mildly interesting edge case: Clearly a pointer that points to at least one valid byte could be used as the src or dest pointer to a call to memcpy(, 0). Would such an aspect be influenced in any ways if the address of operator would be applied around similar expressions? How to force Unity Editor/TestRunner to run at full speed when in background? Dereferencing a null pointer is undefined behavior, typically abnormal program termination. The purpose of that line of code is to read through the current values in the list and strip out any that have become null, there's no null check happening as far as I can tell. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. Not the answer you're looking for? Finally, Clang and Coccinelle are part of the LLVM project, which will define some of the undefined behaviors in C++. It should be an ingrained practice. Example: educators, technical writers, and project/program managers. It can never evaluate to true (unless Equals has been overridden to do something screwy). If you put the code above in a c file, run the analysis, does it report the warning? I would, at the very least, put an assert(q) inside if (code2), but: Ideally you'd stick with that one if/else and put all your logic in there. SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. Which language's style guidelines should be used when writing code that is supposed to be called from another language? May be you need to do this null check much before. How do the interferometers on the drag-free satellite LISA receive power without altering their geodesic trajectory? I'd guess WG14 has considered these questions, but I haven't until now :). Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. It is always true that if E is a function designator or an lvalue that is a valid operand of the unary & operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Before assigning a value you need to allocate a memory and make the pointers to point to that memory location and then assign a value. The above check can't hurt, as I guess you could have a system with a 32-bit size_t that had a ton of memory and had some crazy banking/selector scheme with pointers. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. This is in the key management code which converts passwords. availability of the system. assert(!invalid(p)); // or whatever, bool invalid(const void *p) { Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc. Made code more compliant with other rules. This code also violates ERR33-C. Detect and handle standard library errors. ), Does not guess that return values from malloc(), strchr(), etc., can be NULL (The return value from malloc() is NULL only if there is OOMo and the dev might not care to handle that. If you are working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished. It would be tricky, and they would want WG14 (C working group) to at least bless this change, and more likely, make the analogous change to the C standard. This was potentially problematic, due to the assert on an uninitialized variable. NULL can't point to data. Dereferencing a null pointer is undefined behavior. Setting an incorrect jump target leads to a certain crash if the code is exercised. I suggest that this topic needs to include calloc() and realloc() Refer to Linux man pages online for more enlightenment about malloc(), and friends. While not explicitly mentioning UB, I would infer that *NULL is UB since NULL is not a pointer to an object or function type. What is this brick with a round back and a stud on the side used for? Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. Why the obscure but specific description of Jane Doe II in the original complaint for Westenbroek v. Kappa Kappa Gamma Fraternity? The sk pointer is initialized to tun->sk before checking if tun is a null pointer. You have defined pointers var1 and var2 of type uint64_t and char respectively which are pointing to NULL . This means one of two things: The pointer could in fact be NULL and any dereference prior to that NULL check could result in a NULL pointer dereference, so you need to either do the NULL check sooner or don't deereference at that point. Do you find another previous clarification approach interesting and helpful? This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. That makes sense. in this line you are trying to assign a value 0 to a location pointed by var1 which is NUll location ie invalid address and de-referencing a invalid /Null address will result in crash. Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. Finally, there is the matter of the compliant solution. This fault is buried deep within some complex logic that makes it really hard to track. Connect and share knowledge within a single location that is structured and easy to search. Category. The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. Various developers and code reviewers are struggling also with evolution of the specifications for such programming languages. See C23 (n3096) s6.5.3.2p3: The unary & operator yields the address of its operand. But no where in that particular idiom would a NULL pointer necessarily be deferenced. I believe in this case, either expression would work. Overall, I disagree with her answer, and agree with the StackOverflow response (https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be). CVE-2023-1587 : Avast and AVG Antivirus for Windows were susceptible to How come an array's address is equal to its value in C? When length is zero, it is probably unusable condition for this function. Shouldn't the function check all pointers before dereferencing them or passing them to another function? Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values. Example: tool developers, security researchers, pen-testers, incident response analysts. Ah, gotcha. Because null pointer dereferencing is UB, the if (!tun) check can be elided entirely by the optimizer (since the tun->sk implies that tun must be non-null). Which ability is most related to insanity: Wisdom, Charisma, Constitution, or Intelligence? return p == NULL || (char *)p < &_etext; Thanks for contributing an answer to Stack Overflow! Avast and AVG Antivirus for Windows were susceptible to a NULL pointer dereference issue via RPC-interface. Making statements based on opinion; back them up with references or personal experience. This was the kind of error that most likely would never cause a problem during development but could have wreaked havoc after a release. REVERSE_INULL False Positive "Dereference before NULL check" Asking for help, clarification, or responding to other answers. Specifically, it understands that Equals is meant to test equality, and that you're comparing x to null as if they might be the same (the "check"), but you can't get into Equals (the "path") at all because of the NullReferenceException. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself. The format With two string literals, "SGI_ACL_FILE" and "SGI_ACL_DEFAULT", the addition of the (unsigned char *) cast resulted in sizeof returning 7 (size of pointer minus one), rather than the length of Impacts a highly used used area of our code which could cause problems when running for extended time. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. Why is this claimed dereferencing type-punned pointer warning compiler-specific? Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. What's the rationale for null terminated strings? Variant - a weakness Alternate Terms Relationships . By 'valid pointers' I mean that both src and dest pointers are not null and they both point to non-overlapping arrays containing at least n bytes each. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Configure coverity to check that a declared variable is initialized before usage as a pointer. Small typo nit: "such as if i t pointed to freed memory" meant to say "if it" instead (removing whitespace). This HandleRequest Function evaluates the close before checking the error. rev2023.5.1.43405. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. User without create permission can create a custom object from Managed package using Custom Rest API. View Defect : ScummVM: OVERRUN: C/C++: Memory - illegal accesses: Realy nice catch by Coverity. Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. That interpretation of the standard is not supported universally. This is a matter of style, and also following code walkthrough. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). 565), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Specifically, it understands that Equals is meant to test equality, and that you're comparing x to null as if they might be the same (the "check"), but you can't get into Equals (the "path") at all because of the NullReferenceException. 2005-11-07. Monitor the software for any unexpected behavior. A non-null but invalid pointer passed to memcpy() can indeed cause undefined behavior, but that is not the issue in the noncompliant codethe pointer will either be valid or null. IMHO, the rule title should be changed to something less general. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. . <, [REF-1033] "NULL Pointer Dereference [CWE-476]". Search for vulnerabilities resulting from the violation of this rule on the CERT website. Which language's style guidelines should be used when writing code that is supposed to be called from another language? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. So 'decoded' will always false. * @return a list of vms which are candidates for migration Coverity Scan - Static Analysis So let me be more precise in my wording: I assert that a platform whose memcpy() did anything besides copy zero bytes when given n=0 and valid src and dest pointers was not C-standards-compliant. What's the cheapest way to buy out a sibling's share of our parents house if I have no cash and want to pay less than the appraised value? Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an address inappropriately aligned for the type of object pointed to, and the address of an object after the end of its lifetime. Carnegie Mellon University . It is pretty easy to miss such things when adding a new feature. Yes the ordering matters. how to remove a project from coverity-scan, Remove duplicate results from multiple Coverity runs, Coverity. And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). Pointer members in structs are not checked. What is the symbol (which looks similar to an equals sign) called? It even looked as a false positive at first. Found logically dead code that would never have been accessed. NULL pointer dereferences are frequently resultant from rarely encountered error conditions, since these are most likely to escape detection during the testing phases. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). Allowing it to be removed. The platform does add offsetof( struct_type, member) to input and dereferences that. Hence the error. Network monitor allows remote attackers to cause a denial of service (crash) or execute arbitrary code via malformed packets that cause a NULL pointer dereference. On many platforms, dereferencing a null pointer results inabnormal program termination, but this is not required by the standard. I note with interest, that ISO C does permit &*x when x is null. To learn more, see our tips on writing great answers. Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? This turned out to be a security flaw, now known as CVE-2015-3237. Apple. 33615. If code1 and code2 may both be true, though, then you do have a substantial bug here. I doubt that "length" of zero is a valid parameter, and although there no copy, but we see memory allocation. What does 'They're at four. The description The sk pointer is initialized to tun->sk before checking if tun is a null pointer. is provided for a non-compliant code example.Thus it seems that the arrow operator (member access through pointer) is usually treated also as a dereference operation. An extremely nice thing which was discovered only by Coverity. It is a corner case that would flash once in the blue moon - but with serious impact on the production availability. Agreed. More information is available Please edit the custom filter or select a different filter. Coverity - forward null dereference #1747 - Github Chain: Use of an unimplemented network socket operation pointing to an uninitialized handler function (, Chain: race condition might allow resource to be released before operating on it, leading to NULL dereference, Chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference, Chain: IP and UDP layers each track the same value with different mechanisms that can get out of sync, possibly resulting in a NULL dereference, Chain: uninitialized function pointers can be dereferenced allowing code execution, Chain: improper initialization of memory can lead to NULL dereference, Chain: game server can access player data structures before initialization has happened leading to NULL dereference, Chain: The return value of a function returning a pointer is not checked for success (, Chain: a message having an unknown message type may cause a reference to uninitialized memory resulting in a null pointer dereference (, Chain: unchecked return value can lead to NULL dereference. Hence the error. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. One could argue that all code examples would be redundant with the first pair. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. large number of packets leads to NULL dereference, packet with invalid error status value triggers NULL dereference, Chain: race condition for an argument value, possibly resulting in NULL dereference. It worked normally, but sometimes devices had cryptic types. As a result, the optimizer may remove null . Your assertion is not backed by the wording in the standard, nor by common implementer understanding. Negative index used in the code could result in a totally wrong behavior in the application. 0 is certainly within the 'domain of the function' (a phrase defined by mathematics but not by C11), as copying 0 bytes is well-understood (although silly). Note that it doesn't know how to check for non-heap, non-stack. This defect on our template caused null pointer deferencing in over hundred use cases. Checker. Aaron:I suspect we are talking past each other. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. It modifies the pointed-to data. accesses memory stored at its address. Asking for help, clarification, or responding to other answers. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. Embedded hyperlinks in a thesis or research paper. Coverity complains below message: I do not understand why coverity complains here. Category - a CWE entry that contains a set of other entries that share a common characteristic. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. On such a call, a function that locates a character finds no occurrence, a function that compares two character sequences returns zero, and a function that copies characters copies zero characters. It also reinforces the notion to the reader that any time you see arithmetic in an allocation expression, you need to think about corner-cases. Although not a critical application this prevents a real SQL injection. We were using the wrong "pages in" counter FreeBSD's ZFS port:could cause performance issues.Luckily this is not production code yet. Coverity's suggestion to fix this bug is to use a delete[] deallocator, but the concerned file is in C so that won't work. We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. Right? NULL Pointer Dereference in mruby/mruby- vulnerability database A boy can regenerate, so demons eat him for years. This code also violates ERR33-C. Detect and handle standard library errors. That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). Asking for help, clarification, or responding to other answers. Either the check against null is unnecessary, or there may be a null pointer dereference. It's even called out explicitly in C17 7.24.1p2: Where an argument declared as size_t n specifies the length of the array for a function, n can have the value zero on a call to that function. Thanks for contributing an answer to Stack Overflow! mruby is vulnerable to NULL Pointer. Dates. Thanks for contributing an answer to Stack Overflow! Copy the n-largest files from a certain directory to the current one. repository mruby/mruby prior to 3.2. * Select VMs from the broken affinity group that are running on the same host. Is "I didn't think it was serious" usually a good defence against "duty to rescue"? Running through Coverity reports and it is having issues with the "onsSelectedCredentials.RemoveAll(x => x.Equals(null));" line here, stating "check_after_deref: Null-checking x suggests that it may be null, but it has already been dereferenced on all paths leading to the check." Relatively low, but also relatively hilarious - someone decided to "shut up" a GCC warning in 2006 by putting parentheses around an assignment used as a truth value, but misplaced Impact is low, just wanted to commend you! Then we hit memcpy with length 0. VM {} is NOT a viable candidate for solving affinity group violation situation. Simple deform modifier is deforming my object, xcolor: How to get the complementary color. Coverity is correctly telling you that, albeit in a somewhat indirect way. I have simplified it below (with the first warning)-, The code goes on to do several operations with a_ptr. The idea is not to guarantee validity, but to catch a substantial number of problems that could occur. Possible Null Pointer exception was found in a feature in which I'm the feature owner. Do not use a null in a case where an object is required, https://gcc.gnu.org/gcc-4.9/porting_to.html, ARR30-C. Do not form or use out-of-bounds pointers or array subscripts, Reconsidering pointer dereferences before null pointer checks (with SmPL), understand the source code search pattern, One of the Coccinelle software maintainers expressed opposite development views today, https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be, Prior to 2018-01-12: CERT: Unspecified Relationship, Pointer Casting and Pointer Type Changes [HFC], Dereferencing an out-of-domain pointer [nullref], Section 5.2.18, "Null-Pointer Dereference", Dereferencing null pointers that were not returned by a function. This table shows the weaknesses and high level categories that are related to this weakness. that we haven't considered here: I'd guess null pointers are not valid, even though they point to 0 bytes. Markus:Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. * @param vmToHost vm to host assignments Is there any known 80-bit collision attack? 412-268-5800, If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointer. The exact line that helped in your answer was this - "In this particular case, you're explicitly setting a_ptr to the address of a variable, so it can't possibly be NULL at that point. Synopsys, Inc. | Policy Statement | Contact. At this point we define size as strlen(input_str) + 1. If you want to change the value of your pointer, just do var1 = 0; This listing shows possible areas for which the given weakness could appear. I'll just provide a few references to back up my beliefs. Phew, we're agreed here. Coverity analysis defect 116994: Dereference after null check - MongoDB Only irrelevant information has been removed. What is the symbol (which looks similar to an equals sign) called? Solutions I propose: .. One of the Coccinelle software maintainers expressed opposite development views today. Not the answer you're looking for? In this case, the difference is the assumption thatmalloc() always returns non-nullfor the second NCCE, whereas the first NCCE has themalloc() abstracted away. The occurrence of this wrong index was not seen in the code. He also rips off an arm to use as a sword, Canadian of Polish descent travel to Poland with Canadian passport, assertions usually only apply at debug-time (as I was recently reminded with a runtime crash in a release build that made no sense after all, I have assertion safety everywhere, right?). In the following code, the programmer assumes that the system always has a property named "cmd" defined. To learn more, see our tips on writing great answers. Yeah, I suspect once it's possible to allocate 2+gigs contiguously in amainstream install of a modern OS, we'll see a frenzy of new vulnerabilities come out. I reordered that code example to do all the checks before allocations. Should I re-do this cinched PEX connection? cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". The chunkdata pointer is later used as a destination argument in a call to memcpy(), resulting in user-defined data overwriting memory starting at address 0. Can this be fixed if I reassign the *var1 to NULL again ?? that is linked to a certain type of product, typically involving a specific language or technology. That exception could have rendered the entire feature non operational (And many log messages that Unused value and previous write overwriting found in the defect meant error in algorithm. Coverity found a case where a copy/paste action went wrong. Thanks for this checker. Optimizers are optimizing based on this latitude and have been for years. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Not sure if this is directly related to the error/warning you get but in general I think you should rather use, C# Coverity giving "Dereference before null check (REVERSE_INULL)" on a RemoveAll call to remove null entries from a list, How a top-ranked engineering school reimagined CS curriculum (Ep. Believing that dereferencing NULL shouldn't crash the system doesn't make it true. Synopsys, Inc. | Policy Statement | Contact, // Create a set of all VMs in affinity groups, // There is no need to migrate when no collision was detected. LANG.MEM.NPDLANG.STRUCT.NTADLANG.STRUCT.UPD, Null pointer dereferenceNull test after dereferenceUnchecked parameter dereference, Can detect violations of this rule. C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. View - a subset of CWE entries that provides a way of examining CWE content. In this scenario, by the time, I come in 'cond2', I already have 'q' set. Connect and share knowledge within a single location that is structured and easy to search. The expression x.Equals(null) will throw NullReferenceException if x is null. Coverity is giving you a warning because you are in fact doing a NULL check: Here, a_ptr is evaluated in a boolean context. Can I use the spell Immovable Object to create a castle which floats above the clouds? DATABASE RESOURCES PRICING ABOUT US. NIST. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. c - Coverity issue : Explicit Null dereferenced - Stack Overflow Parabolic, suborbital and ballistic trajectories all follow elliptic paths. Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. This noncompliant code example is derived from a real-world example taken from a vulnerable version of the libpng library as deployed on a popular ARM-based cell phone [Jack 2007]. 2012-09-11. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Coverity - Explicit null dereferenced (FORWARD_NULL) in contentResolver.delete(), Coverity report meanings - PW.INCLUDE_RECURSION, Extracting coverity .csv file from coverity server, C# Coverity giving "Dereference before null check (REVERSE_INULL)" on a RemoveAll call to remove null entries from a list.
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