This code will definitely crash due to a null pointer dereference in certain cases. I've changed it to say null pointer instead of invalid pointer. 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. NULL Pointer Dereference in mruby/mruby- vulnerability database It can never evaluate to true (unless Equals has been overridden to do something screwy). In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. Variant - a weakness Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). Asking for help, clarification, or responding to other answers. Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. Coverity is correctly telling you that, albeit in a somewhat indirect way. OS allows remote attackers to cause a denial of service (crash from null dereference) or execute arbitrary code via a crafted request during authentication protocol selection. If an attacker can control the program's environment so that "cmd" is not defined, the program throws a NULL pointer exception when it attempts to call the trim() method. 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. This table shows the weaknesses and high level categories that are related to this weakness. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? Find centralized, trusted content and collaborate around the technologies you use most. 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. It is a corner case that would flash once in the blue moon - but with serious impact on the production availability. LANG.MEM.NPDLANG.STRUCT.NTADLANG.STRUCT.UPD, Null pointer dereferenceNull test after dereferenceUnchecked parameter dereference, Can detect violations of this rule. This is the intention for the referenced small script of the semantic patch language. May it be expected that the address of operator will eventually be evaluated only after a pointer dereference for a desirable access to a data structure member? */. 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. 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. It would have been terrible to A simple decrement that wraps around causing an array overflow on lsm->lsm_oinfo[i[. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. At best ISO C is under-specified in this regard, and perhaps should explicitly say so. And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). It does not give the pointer a new value. 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. that is linked to a certain type of product, typically involving a specific language or technology. Then we hit memcpy with length 0. it may still not be enough to satisfy Coverity. Finally, Clang and Coccinelle are part of the LLVM project, which will define some of the undefined behaviors in C++. 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. I doubt that "length" of zero is a valid parameter, and although there no copy, but we see memory allocation. While not explicitly mentioning UB, I would infer that *NULL is UB since NULL is not a pointer to an object or function type. I would therefore assert that a platform whose memcpy() did anything besides a no-op when given n=0 and valid source/destination pointers was not C-standards-compliant. Dereferencing a pointer that might be null " findVmViolatingPositiveAg(affinityGroup, vmToHost) " when calling " getVmsByIds . Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. The null pointer check for writing or dereferencing should be a compiler flag or library setting. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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. Customer's opinion is that it is always a good practice to check a pointer for a NULL Value before freeing it. It looks like a logic bug, which can cause a memory leaking. Coverity Scan - Static Analysis To subscribe to this RSS feed, copy and paste this URL into your RSS reader. valgrind wasnt that usefull because of its slowness. This Android application has registered to handle a URL when sent an intent: The application assumes the URL will always be included in the intent. patch id. In this scenario, by the time, I come in 'cond2', I already have 'q' set. As a result, the optimizer may remove null . Chains can involve more than two weaknesses, and in some cases, they might have a tree-like structure. ", Getting warning - Dereferencing before possibly being null in C code, How a top-ranked engineering school reimagined CS curriculum (Ep. 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. Various developers and code reviewers are struggling also with evolution of the specifications for such programming languages. 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. In that case, if you want to change the value of the pointed-to data, well, have the pointer point to some writeable memory first! (I think you cover that in a different rule.) Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. Dereferencing a null pointer is undefined behavior. Is there any known 80-bit collision attack? The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase. Asking for help, clarification, or responding to other answers. The issue was fixed with Avast and AVG Antivirus version 22.11 Publish Date : 2023-04-19 Last Update Date : 2023-04-19 Collapse All Expand All Select Select&Copy Scroll To Vendor . Not the answer you're looking for? Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? Off by one error: It is the third example. I'll add that right now, but I feel it's pointless, since it will only clutter up the question. This has been there for decade, and was shipped in a real product. It also adds assertions to document that certain other pointers must not be null. to non-modifiable storage when the corresponding parameter is not const-qualified) or a type (after default argument promotion) not expected by a function with a variable number of arguments, the behavior is undefined. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Do you find another previous clarification approach interesting and helpful? Coverity Prevent cannot discover all violations of this rule, so further verification is necessary, Detects when NULL is dereferenced (Array of pointers is not checked. See C23 (n3096) s6.5.3.2p3: The unary & operator yields the address of its operand. I added a comment to explain that SIZE_MAX is the limit of size_t. Check the results of all functions that return a value and verify that the value is non-null before acting upon it. It calls x.Equals() a "dereference", unfortunately using C/C++ terminology (for historical reasons). VM {} is NOT a viable candidate for solving affinity group violation situation. 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. I have simplified it below (with the first warning)-, The code goes on to do several operations with a_ptr. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. Coverity scan helps our developers finding issues like these. * Select VMs from the broken affinity group that are running on the same host. and Gary McGraw. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Is there any known 80-bit collision attack? How NULL access (FORWARD_NULL) is reported in Coverity - Synopsys Thanks! Shouldn't the function check all pointers before dereferencing them or passing them to another function? 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. So the SIZE_MAX check was unnecessary. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. * @param affinityGroup broken affinity rule The platform is listed along with how frequently the given weakness appears for that instance. Thanks for contributing an answer to Stack Overflow! Variable "var" was uninitialized, then function that was supposed to fill it in was called. A boy can regenerate, so demons eat him for years. That's true. What's the rationale for null terminated strings? . Connect and share knowledge within a single location that is structured and easy to search. Solutions I propose: .. If input is null, that is technically not a null dereference, but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. {"serverDuration": 277, "requestCorrelationId": "e2a1d936a1543fbd"}, EXP34-C. Do not dereference null pointers, Clever Attack Exploits Fully-Patched Linux Kernel, ERR33-C. Detect and handle standard library errors, one compliant and one non-compliant example, CERT Oracle Secure Coding Standard for Java, EXP01-J. Optimizers are optimizing based on this latitude and have been for years. This was potentially problematic, due to the assert on an uninitialized variable. And in this step. Developer Description. parsing /proc/self/maps under linux) one might find out whether the pointer points into mapped memory, but this is still not a guarantee of validity because it is very coarse-grained see again the above example. Making statements based on opinion; back them up with references or personal experience. Example: tool developers, security researchers, pen-testers, incident response analysts. I believe that dereferencing NULL should not crash the system, should not allow a write to a NULL pointer area, but should always set errno, If I am a hacker, could I trap a null failure that would force a memory dump. Coverity analysis defect 116994: Dereference after null check - MongoDB Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? unity3d - C# Coverity giving "Dereference before null check (REVERSE If all pointers that could have been modified are sanity-checked previous to use, nearly all NULL pointer dereferences can be prevented. availability of the system. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. mruby is vulnerable to NULL Pointer. Because null pointer dereferencing is undefined behavior, the compiler (GCC in this case) can optimize away the if (!tun) check because it is performed after tun->sk is accessed, implying that tun is non-null. In Coverity, FORWARD_NULL reports defects when there are enough evidences to be sure the null access will (can) happen. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. Dereferencing a null pointer is undefined behavior, typically abnormal program termination. 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. If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). So before writing anything to some memory location memory has to allocated to the pointer. VM {} is a viable candidate for solving affinity group violation situation. If you want to change the value of your pointer, just do. And Coverity will tend to interpret your code rather than reading your mind. We didn't figure ourselves where those threading issues came from and tried to hide them with hacks. <, [REF-1031] "Null pointer / Null dereferencing". specifies the length of the array for a function. In the following code, the programmer assumes that the system always has a property named "cmd" defined. User without create permission can create a custom object from Managed package using Custom Rest API. <<< CID 102061: Null pointer dereferences REVERSE_INULL <<< Null-checking " doc_bv " suggests that it may be null, but it has already been dereferenced on all paths leading to the check. Coverity Scan - Static Analysis Why refined oil is cheaper than cold press oil? I reordered that code example to do all the checks before allocations. then the UB is not in your code, you just may be searching for code with potential UB. In 5e D&D and Grim Hollow, how does the Specter transformation affect a human PC in regards to the 'undead' characteristics and spells? This compliant solution ensures that both input_str andthe pointer returned by malloc() are not null: This noncompliant code example is from a version of drivers/net/tun.c and affects Linux kernel 2.6.30 [Goodin 2009]: The sk pointer is initialized to tun->sk before checking if tun is a null pointer. This HandleRequest Function evaluates the close before checking the error. This check identifies such situation by checking all possible paths where such NULL dereferences can occur. Separate it into a different function that you can call. Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. Should I re-do this cinched PEX connection? That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). which bolsters my assertion that x->member dereferences x (or at least an offset of x). In particular, ROSE ensures that any pointer returned by malloc(), calloc(), or realloc() is first checked for NULL before being used (otherwise, it is free()-ed). If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Why does the second compliant example permit using possibly-null pointers? It also permits &x[y] to translate to x + y, but that is still UB if x is null because of ARR38-C. ISO C just has no similar wording for x->member. It seems that my understanding needs also to grow for such information. Making statements based on opinion; back them up with references or personal experience. . NULL Pointer Dereference in mrb_vm_exec with super in GitHub. 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. Synopsys, Inc. | Policy Statement | Contact. 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. Coverity Scan - Static Analysis :). Correct; a null pointer is not a valid pointer for the C library functions. The two languages try to maximize compatibility, . SIZE_MAX is the largest possible value that a size_t could take, so it is not possible to have anything larger than SIZE_MAX. I note with interest, that ISO C does permit &*x when x is null. This information is often useful in understanding where a weakness fits within the context of external information sources. You need to show more code along with what static analysis tool you are using for us to be able to give an answer to you. Configure coverity to check that a declared variable is initialized before usage as a pointer. It evaluates to true if a_ptr is not NULL. DATABASE RESOURCES PRICING ABOUT US. What is the symbol (which looks similar to an equals sign) called? Finally, there is the matter of the compliant solution. Will the ordering matter a bit more for the safe evaluation of involved expressions? 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. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Full description here: http://curl.haxx.se/docs/adv_20150617B.html It could make a malicious server fool a client to send off data from Prototypical copy-paste error.