The final NCCE is actually more insidious than it seems at first. I note with interest, that ISO C does permit &*x when x is null. Why did DOS-based Windows require HIMEM.SYS to boot? 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. (where the weakness is a quality issue that might indirectly make it easier to introduce security-relevant weaknesses or make them more difficult to detect). Made code more compliant with other rules. that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. Copyright 20062023, The MITRE Corporation. For users who are interested in more notional aspects of a weakness. The expression x.Equals(null) will throw NullReferenceException if x is null. The different Modes of Introduction provide information about how and when this weakness may be introduced. 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. Then we hit memcpy with length 0. It should be an ingrained practice. I believe in this case, either expression would work. Can I use an 11 watt LED bulb in a lamp rated for 8.6 watts maximum? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Finally, Clang and Coccinelle are part of the LLVM project, which will define some of the undefined behaviors in C++. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Possibly Clang/LLVM may choose to always return a valid value for &NULL->member. Parabolic, suborbital and ballistic trajectories all follow elliptic paths. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Horizontal and vertical centering in xltabular. 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. can have the value zero on a call to that function. 33615. 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 is kind of funny, though. Null pointer dereferences. Example: tool developers, security researchers. Description. The correct idiom is to only allocate storage if the pointer is currently NULL. Game allows remote attackers to cause a denial of service (server crash) via a missing argument, which triggers a null pointer dereference. For users who are mapping an issue to CWE/CAPEC IDs, i.e., finding the most appropriate CWE for a specific issue (e.g., a CVE record). Pittsburgh, PA 15213-2612 It evaluates to true if a_ptr is not NULL. Embedded hyperlinks in a thesis or research paper, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). NULL pointer dereferences are frequently resultant from rarely encountered error conditions, since these are most likely to escape detection during the testing phases. 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. Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference. To fix the bug in the code and also make Coverity happy, as suggested by derHugo in a comment, change the RemoveAll line to something like this: Thanks for contributing an answer to Stack Overflow! A common memory-leak idiom, is reallocating storage and assigning its address to a pointer that already points to allocated storage. This vulnerability is capable. This information is often useful in understanding where a weakness fits within the context of external information sources. Asking for help, clarification, or responding to other answers. As a result, the optimizer may remove null . 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. Using platform-specific means (e.g. Solution 1, it looks like, today's solution tomorrow's problem. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. specifies the length of the array for a function. It would have been terrible to A simple decrement that wraps around causing an array overflow on lsm->lsm_oinfo[i[. That makes sense. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. What is the symbol (which looks similar to an equals sign) called? This was the kind of error that most likely would never cause a problem during development but could have wreaked havoc after a release. which bolsters my assertion that x->member dereferences x (or at least an offset of x). it may still not be enough to satisfy Coverity. 0->member is undefined behavior. More information is available Please edit the custom filter or select a different filter. In 5e D&D and Grim Hollow, how does the Specter transformation affect a human PC in regards to the 'undead' characteristics and spells? 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. How a top-ranked engineering school reimagined CS curriculum (Ep. I find it interesting in this case how you think in another direction. Buffer overflow and possibly corrupting the module database. Various developers and code reviewers are struggling also with evolution of the specifications for such programming languages. If malloc() fails, it returns a null pointer that is assigned to c_str. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. Thank you for clarifying your assertion until I understood it properly. 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). is undefined behavior (UB) if input does not actually point to a valid struct. I added an assertion to that compliant code example. Thanks for contributing an answer to Stack Overflow! This code also violates ERR33-C. Detect and handle standard library errors. If you want to change the value of your pointer, just do var1 = 0; race condition causes a table to be corrupted if a timer activates while it is being modified, leading to resultant NULL dereference; also involves locking. NULL Pointer Dereference in mrb_vm_exec with super in GitHub. The two languages try to maximize compatibility, . 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. First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. Why are players required to record the moves in World Championship Classical games? Aaron:I suspect we are talking past each other. This pointer was the resaon of a memory leak Realy nice catch by Coverity. Wikipedia. Software Engineering Institute To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Making statements based on opinion; back them up with references or personal experience. String URL = intent.getStringExtra("URLToOpen"); func HandleRequest(client http.Client, request *http.Request) (*http.Response, error) {. I'm learning and will appreciate any help. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Asside - I would suggest initialising your pointers to, It's impossible to tell from that code whether. I have simplified it below (with the first warning)-, The code goes on to do several operations with a_ptr. Expressions (EXP), SEI CERT C Coding Standard - Guidelines 03. Setting an incorrect jump target leads to a certain crash if the code is exercised. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. The platform is listed along with how frequently the given weakness appears for that instance. Created: Jan 26 2021 02:47:29 PM UTC Updated: Jan 26 2021 10:07:21 PM UTC . extern char _etext; This is not a perfect solution, since 100% accuracy and coverage are not feasible. Null pointer dereferences: This code will definitely crash due to a null pointer dereference in certain cases.. View Defect : wazuh/ossec-wazuh: USE_AFTER_FREE: C/C++: Memory - illegal accesses: This pointer was the resaon of a memory leak. Why don't we use the 7805 for car phone chargers? A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. New feature implementation got stuck for days because old code had obscure implementation which caused debuging nightmare. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. @HemantBhargava - you may know that, but the code you have shown us does not ensure that. Copy the n-largest files from a certain directory to the current one. 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. Assign an array of Swift strings to a C structure variable taking a char ** value. Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. accesses memory stored at its address. Similarly, if the operand is the result of a [] operator, neither the & operator nor the unary * that is implied by the [] is evaluated and the result is as if the & operator were removed and the [] operator were changed to a + operator. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. This compliant solution ensures that the pointer returned by png_malloc() is not null. 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. The issue is: memcpy() and friends do not explicitly state that a null pointer is a valid pointer value, even if the number of bytes to copy is 0. . Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). Which language's style guidelines should be used when writing code that is supposed to be called from another language? ROSE does not handle cases where an allocation is assigned to an lvalue that is not a variable (such as a struct member or C++ function call returning a reference), Finds instances where a pointer is checked against NULL and then later dereferenced, Identifies functions that can return a null pointer but are not checked, Identifies code that dereferences a pointer and then checks the pointer against NULL, Can find the instances where NULL is explicitly dereferenced or a pointer is checked againstNULL but then dereferenced anyway. Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? <. One of the Coccinelle software maintainers expressed opposite development views today. We should Zoom if you wish to talk more. While not explicitly mentioning UB, I would infer that *NULL is UB since NULL is not a pointer to an object or function type. Developer Description. What is the symbol (which looks similar to an equals sign) called? Fixed by setting name to Oh joy. Dates. Which ability is most related to insanity: Wisdom, Charisma, Constitution, or Intelligence? 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. Hence the error. 2005-11-07. Not the answer you're looking for? Either the check against null is unnecessary, or there may be a null pointer dereference. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Simple deform modifier is deforming my object, xcolor: How to get the complementary color. . This bug was quite hard to spot! This listing shows possible areas for which the given weakness could appear. Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. I'm getting a warning while doing a Static Analysis (SA) on my code. Consider the following example of a typical client server exchange. What is it that I did not understand? Asking for help, clarification, or responding to other answers. Synopsys, Inc. | Policy Statement | Contact. Finally, there is the matter of the compliant solution. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? I would also guess that pointers that point to the one-past-the-end of an array are also invalid. Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. Is this a false positive from Coverity or should I do something to fix this? The NULL check is unnecessary because the pointer can't be NULL, so the NULL check should be removed. Event var_deref_model: | Passing null pointer "master_uri_env" to "operator =", which dereferences it. Carnegie Mellon University Typical "easy to spot if you know there is a problem error". For users who want to customize what details are displayed. 2012-09-11. 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. 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. Why does Acts not mention the deaths of Peter and Paul? Can this be fixed if I reassign the *var1 to NULL again ?? What REALLY happens when you don't free after malloc before program termination? then the UB is not in your code, you just may be searching for code with potential UB. NIST. We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. Standing by. An extremely nice thing which was discovered only by Coverity. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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. Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? In the first compliant example it's useless to do allocation if the essential pointer user_data is NULL. Dereferencing a null pointer is undefined behavior. Which language's style guidelines should be used when writing code that is supposed to be called from another language? 2019-07-15. 2005. Thanks, David! 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. The occurrence of this wrong index was not seen in the code. 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. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented.
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