By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Apple. 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. It would cause game actors to teleport to the wrong coordinates. very useful to find this very horrible bug in this case, we're using a pointer to memory which is not guaranteed to be zero, and potentially corrupting the malloc arena in the process. I'm learning and will appreciate any help. More information is available Please edit the custom filter or select a different filter. How come an array's address is equal to its value in C? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. (C11, S7.24.2.1). Will the ordering matter a bit more for the safe evaluation of involved expressions? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The 2nd NCCE/CS pair seems redundant with the first NCCE/CS pair. I guess you could write a proposal to modify the C Standard, but our coding standard is meant to provide guidance for the existing language. Would My Planets Blue Sun Kill Earth-Life? Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference. rev2023.5.1.43405. Thanks! At one point later, I get another warning: It seems like the line a_ptr->ptr = NULL is deemed incorrect/dangerous. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); Consider the following example of a typical client server exchange. patch id. It depends on the specific details, but in general, taking the address of any valid memory is OK. One weakness, X, can directly create the conditions that are necessary to cause another weakness, Y, to enter a vulnerable condition. This code also violates ERR33-C. Detect and handle standard library errors. Security Intelligence; Non-intrusive assessment; Developers SDK; Database . Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. If you want to change the value of your pointer, just do var1 = 0; May be you need to do this null check much before. 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. 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. Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage. I'll just provide a few references to back up my beliefs. 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). In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. A boy can regenerate, so demons eat him for years. Embedded hyperlinks in a thesis or research paper, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). 2019-07-15. I suppose we can check that that is not null, but we cannot check that it is valid (in any portable way). 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. And this error has been in the codebase for the last 9 Coverty scan correctly understood the logic of this code, and reported that the loop condition is wrong. This fault is buried deep within some complex logic that makes it really hard to track. It does not give the pointer a new value. 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. Did the drapes in old theatres actually say "ASBESTOS" on them? 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. Otherwise, the result is a pointer to the object or function designated by its operand. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. 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. 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. return p == NULL || (char *)p < &_etext; c - Coverity issue : Explicit Null dereferenced - Stack Overflow Parabolic, suborbital and ballistic trajectories all follow elliptic paths. (In contrast, the case of passing 0 bytes to malloc is addressed in C11.) 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). Many modern techniques use data flow analysis to minimize the number of false positives. What should I follow, if two altimeters show different altitudes? Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? 0->member is undefined behavior. then the UB is not in your code, you just may be searching for code with potential UB. As a result, the optimizer may remove null . In my experience, there are reasons to check for a NULL pointer other than dereferencing it. Yes the ordering matters. This listing shows possible areas for which the given weakness could appear. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. How to remove elements from a generic list while iterating over it? Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. This HandleRequest Function evaluates the close before checking the error. C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. This has been there for decade, and was shipped in a real product. Which language's style guidelines should be used when writing code that is supposed to be called from another language? It should be an ingrained practice. Improve INSERT-per-second performance of SQLite. However there is no portable way to verify that the pointer is valid, other than checking for null. Since SIZE_MAX represents the largest possible object, the largest possible string would then be SIZE_MAX-1 characters long (excluding '\0'). Is "I didn't think it was serious" usually a good defence against "duty to rescue"? In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution. See the "Null pointer checks may be optimized away more aggressively" section inhttps://gcc.gnu.org/gcc-4.9/porting_to.htmlas an example with one common implementation. How to force Unity Editor/TestRunner to run at full speed when in background? Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. Episode about a group who book passage on a space ship controlled by an AI, who turns out to be a human who can't leave his ship? FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. Making statements based on opinion; back them up with references or personal experience. Making statements based on opinion; back them up with references or personal experience. Configure coverity to check that a declared variable is initialized before usage as a pointer. Can I use the spell Immovable Object to create a castle which floats above the clouds? 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. "Signpost" puzzle from Tatham's collection. CWE, CWSS, CWRAF, and the CWE logo are trademarks of The MITRE Corporation. This check identifies such situation by checking all possible paths where such NULL dereferences can occur. Hence the error. . void host_lookup(char *user_supplied_addr){, if("com.example.URLHandler.openURL".equals(intent.getAction())) {. My guess is it is telling you "you are doing the NULL check now, but you have already dereferenced it before. 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! That makes sense. 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. * It evaluates to true if a_ptr is not NULL. Optimizers are optimizing based on this latitude and have been for years. This vulnerability is capable. Good question! 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. FORWARD_NULL. Null reference creation and null pointer dereference You have defined pointers var1 and var2 of type uint64_t and char respectively which are pointing to NULL . Would you like to help any further according to different understanding and expectations for affected implementation details. This compliant solution ensures that the pointer returned by png_malloc() is not null. Canadian of Polish descent travel to Poland with Canadian passport. 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]. * @param vmToHost vm to host assignments Dereferencing a null pointer is undefined behavior, typically abnormal program termination. It calls x.Equals() a "dereference", unfortunately using C/C++ terminology (for historical reasons). Without coverity i probably would not have found this copy&paste error. Developer Description. and Gary McGraw. you are trying to make your var1 to point to the same location as that of var2 and casting it to uint64_t.So from the above two sections var1 and var2 are pointing to NULL pointer ie nothing in simple terms. And in this case, there is no pointed-to data. 4500 Fifth Avenue cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". Monitor the software for any unexpected behavior. }. rev2023.5.1.43405. Should I re-do this cinched PEX connection? 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. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. Right? Can this be fixed if I reassign the *var1 to NULL again. Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? We should Zoom if you wish to talk more. . CVE-2023-1587 : Avast and AVG Antivirus for Windows were susceptible to If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. Check the results of all functions that return a value and verify that the value is non-null before acting upon it. 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? Assign an array of Swift strings to a C structure variable taking a char ** value. Is this a false positive from Coverity or should I do something to fix this? See C23 (n3096) s6.5.3.2p3: The unary & operator yields the address of its operand. It modifies the pointed-to data. So before writing anything to some memory location memory has to allocated to the pointer. It worked normally, but sometimes devices had cryptic types. We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. Why refined oil is cheaper than cold press oil? This is the intention for the referenced small script of the semantic patch language. It modifies the pointed-to data. Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. 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. . Various developers and code reviewers are struggling also with evolution of the specifications for such programming languages. <, [REF-1031] "Null pointer / Null dereferencing". 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. this patch have merged in upstream master branch. Buffer overflow difficult to find by reading the code that would result a crash if path is too long. Coverity Scan - Static Analysis For users who wish to see all available information for the CWE/CAPEC entry. I've posted an example for the sake of completion-. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. ), 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. 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 user_data pointer could be invalid in other ways, such as pointing to freed memory. Coverity Scan - Static Analysis This compliant solution eliminates the null pointer deference by initializing sk to tun->sk following the null pointer check. ), [REF-6] Katrina Tsipenyuk, Brian Chess This one is pretty awesome. mruby is vulnerable to NULL Pointer. What is it that I did not understand? . 0 is a valid value as far as memcpy() is concerned, and malloc() has special language concerning malloc(0). REVERSE_INULL False Positive "Dereference before NULL check" At this point we define size as strlen(input_str) + 1. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. In Coverity, FORWARD_NULL reports defects when there are enough evidences to be sure the null access will (can) happen. To learn more, see our tips on writing great answers. If you put the code above in a c file, run the analysis, does it report the warning? This fault is buried deep within some complex logic that makes it really hard to track. Fixed by setting name to Oh joy. I'd really love to know why I'm being downvoted. This does not have any impact, because it is just an assert. 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! <, [REF-1032] "Null Reference Creation and Null Pointer Dereference". It is kind of funny, though. This bug ONLY surfaces when debugging or running the program with her verbosity. To learn more, see our tips on writing great answers. Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. Why does Acts not mention the deaths of Peter and Paul? that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. 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 . "Signpost" puzzle from Tatham's collection, Image of minimal degree representation of quasisimple group unique up to conjugacy. 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. Dates. 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). The standard will simply copy 0 byteswhich is essentially a no-op. 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. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. 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. 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. 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. This table shows the weaknesses and high level categories that are related to this weakness. For users who are interested in more notional aspects of a weakness. What does 'They're at four. Not the answer you're looking for? .. Would it be ok if I write !cond1 just like this: Logically, based on what you've said, and assuming that code1 and code2 are mutually exclusive, this is a false positive. COVERITY checker description | The STAR experiment NULL Pointer Dereference in mrb_vm_exec with super in Additionally, if input_str is a null pointer, the call to strlen() dereferences a null pointer, also resulting in undefined behavior. And Coverity will tend to interpret your code rather than reading your mind. Loading. NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). Copyright 20062023, The MITRE Corporation. Would such an aspect be influenced in any ways if the address of operator would be applied around similar expressions? WG21 (the C++ working group) may wish to define 0->y, and they are within their right to do so. Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. Why are players required to record the moves in World Championship Classical games? I find it interesting in this case how you think in another direction. For users who want to customize what details are displayed. Coverity is correctly telling you that, albeit in a somewhat indirect way. As a result, this noncompliant code example is vulnerable to a null pointer dereference exploit, because null pointer dereferencing can be permitted on several platforms, for example, by using mmap(2) with the MAP_FIXED flag on Linux and Mac OS X, or by using the shmat() POSIX function with the SHM_RND flag [Liu 2009]. Thanks for contributing an answer to Stack Overflow! Variant - a weakness 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. This is in the key management code which converts passwords. If code1 and code2 may both be true, though, then you do have a substantial bug here. I'm sorry if I have misunderstood the intent in your question. int changed to size_t and if size_t parameter's is zero, allocate one word. 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. In your code example, the p1my_item will be evaluated before t he & operator, and so this rule is violated, although you are really trying to do pointer arithmetic rather than see what the pointer points to. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called. 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. The two languages try to maximize compatibility, . A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. Do you find another previous clarification approach interesting and helpful? Hence the error. CPE Name Name Version; mruby: 3.1.0: Products. Coverity complains below message: CID 25469 (#1 of 1): Explicit null dereferenced (FORWARD_NULL) 9. var_deref_op: Dereferencing null pointer q. I do not understand why coverity complains here. Example: tool developers, security researchers, pen-testers, incident response analysts. I reordered that code example to do all the checks before allocations. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? 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. 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. valgrind wasnt that usefull because of its slowness. Could I capture, and I would be able to glean much security information from the dump? If malloc() fails, it returns a null pointer that is assigned to c_str. The libpng library allows applications to read, create, and manipulate PNG (Portable Network Graphics) raster image files. Dereferencing a null pointer is undefined behavior. In this noncompliant code example, input_str is copied into dynamically allocated memory referenced by c_str. Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. 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. Event var_deref_model: | Passing null pointer "master_uri_env" to "operator =", which dereferences it. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. It is pretty easy to miss such things when adding a new feature. <<< 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. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. 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. second, a de-reference of that variable. Typical "easy to spot if you know there is a problem error". uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). I'm getting a warning while doing a Static Analysis (SA) on my code. of making the mruby interpreter crash, thus affecting the. It's not them. The final NCCE is actually more insidious than it seems at first. 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. On many platforms, dereferencing a null pointer results inabnormal program termination, but this is not required by the standard. Description. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. Thanks, David! Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. Thanks for contributing an answer to Stack Overflow! This bug was quite hard to spot! Would you become interested in a related clarification approach for a discussion topic like . What's the rationale for null terminated strings? I suggest that this topic needs to include calloc() and realloc() Refer to Linux man pages online for more enlightenment about malloc(), and friends. Find centralized, trusted content and collaborate around the technologies you use most. If a user supplies a malformed request or violates the client policy, the Do method can return a nil response and a non-nil err. 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! This information is often useful in understanding where a weakness fits within the context of external information sources. The issue of passing n=0 to memcpy() is distinct from null or invalid pointers. Only irrelevant information has been removed. which bolsters my assertion that x->member dereferences x (or at least an offset of x). That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). In this scenario, by the time, I come in 'cond2', I already have 'q' set.
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