coverity null pointer dereference

Possible Null Pointer exception was found in a feature in which I'm the feature owner. This compliant solution ensures that the pointer returned by png_malloc() is not null. cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". mruby is vulnerable to NULL Pointer Dereference Affected Software. The expression x.Equals(null) will throw NullReferenceException if x is null. valgrind wasnt that usefull because of its slowness. Canadian of Polish descent travel to Poland with Canadian passport. Not the answer you're looking for? 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. The libpng library implements its own wrapper to malloc() that returns a null pointer on error or on being passed a 0-byte-length argument. Connect and share knowledge within a single location that is structured and easy to search. 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. The choice could be made to use a language that is not susceptible to these issues. Improve INSERT-per-second performance of SQLite. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. "Signpost" puzzle from Tatham's collection, Image of minimal degree representation of quasisimple group unique up to conjugacy. In the first compliant example it's useless to do allocation if the essential pointer user_data is NULL. Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). Buffer overflow difficult to find by reading the code that would result a crash if path is too long. I reordered that code example to do all the checks before allocations. with solve of this bug problems have gone. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. This rule applies to all null pointers, regardless of which function returned them. Parabolic, suborbital and ballistic trajectories all follow elliptic paths. 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. I've posted an example for the sake of completion-. If input is null, that is technically not a null dereference. 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. I added a comment to explain that SIZE_MAX is the limit of size_t. 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. I would also guess that pointers that point to the one-past-the-end of an array are also invalid. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. It modifies the pointed-to data. What does 'They're at four. In the following code, the programmer assumes that the system always has a property named "cmd" defined. Agreed. 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." FORWARD_NULL. Solutions I propose: .. uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. It even looked as a false positive at first. Found logically dead code that would never have been accessed. One situation this can happen is when the pointer has been checked against NULL and is dereferenced later. This is not a perfect solution, since 100% accuracy and coverage are not feasible. This fault is buried deep within some complex logic that makes it really hard to track. To learn more, see our tips on writing great answers. VM {} is a viable candidate for solving affinity group violation situation. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Developer Description. it may still not be enough to satisfy Coverity. Isn't easier just to check valid range of length? 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? /** Making statements based on opinion; back them up with references or personal experience. The final NCCE is actually more insidious than it seems at first. 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? Why is this claimed dereferencing type-punned pointer warning compiler-specific? 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. 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. I'd guess null pointers are not valid, even though they point to 0 bytes. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? Where does the version of Hamapil that is different from the Gemara come from? What are the arguments for/against anonymous authorship of the Gospels, Two MacBook Pro with same model number (A1286) but different year, Simple deform modifier is deforming my object. The platform is listed along with how frequently the given weakness appears for that instance. assert(!invalid(p)); // or whatever, bool invalid(const void *p) { Thanks for this checker. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. More specific than a Base weakness. 33615. Likewise, pointers to freed memory are not valid. Coverity is correctly telling you that, albeit in a somewhat indirect way. Hence the error. 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. 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. 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. Identify error conditions that are not likely to occur during normal usage and trigger them. NULL can't point to data. ", Getting warning - Dereferencing before possibly being null in C code, How a top-ranked engineering school reimagined CS curriculum (Ep. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. The code processes a physics modification option line given either from the command line or file. In this noncompliant code example, input_str is copied into dynamically allocated memory referenced by c_str. 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. 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. This information is often useful in understanding where a weakness fits within the context of external information sources. This was potentially problematic, due to the assert on an uninitialized variable. Setting an incorrect jump target leads to a certain crash if the code is exercised. A pointer should be made to point to some valid memory location before writing something to it. Do you find another previous clarification approach interesting and helpful? If your code examples are simply searching for instances of C code of this nature. What is the symbol (which looks similar to an equals sign) called? The null pointer check for writing or dereferencing should be a compiler flag or library setting. 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. *var1 = 0; this dereferences the pointer, i.e. <, [REF-1033] "NULL Pointer Dereference [CWE-476]". This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. 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. Passing a null pointer tomemcpy() would produce undefined behavior, even if the number of bytes to copy were 0. When this happens, CWE refers to X as "primary" to Y, and Y is "resultant" from X. Yes the ordering matters. The question is concise, clear, to-the-point and logical. This means one of two things: 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. This turned out to be a security flaw, now known as CVE-2015-3237. I suppose we can check that that is not null, but we cannot check that it is valid (in any portable way). This one alone We had some spurious hangs and never knew why. 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. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. * @return a list of vms which are candidates for migration Connect and share knowledge within a single location that is structured and easy to search. While there are no complete fixes aside from conscientious programming, the following steps will go a long way to ensure that NULL pointer dereferences do not occur. Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. This is a matter of style, and also following code walkthrough. The sk pointer is initialized to tun->sk before checking if tun is a null pointer. The platform does add offsetof( struct_type, member) to input and dereferences that. This defect on our template caused null pointer deferencing in over hundred use cases. Not the answer you're looking for? 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. . 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 listing shows possible areas for which the given weakness could appear. 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. A common memory-leak idiom, is reallocating storage and assigning its address to a pointer that already points to allocated storage. is undefined behavior (UB) if input does not actually point to a valid struct. c - Coverity issue : Explicit Null dereferenced - Stack Overflow Configure coverity to check that a declared variable is initialized before usage as a pointer. Otherwise, the result is a pointer to the object or function designated by its operand. Simple and excellent job. Separate it into a different function that you can call. :). COVERITY checker description | The STAR experiment An extremely nice thing which was discovered only by Coverity. "Signpost" puzzle from Tatham's collection. It seems that my understanding needs also to grow for such information. Coverity analysis defect 116994: Dereference after null check - MongoDB To learn more, see our tips on writing great answers. 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. The 4gig boundary will probably be important too with unsigned int in LP64, but since size_t will be 64-bit, there will have to be some truncation that compilers will be able to warn on. Checker. . 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. Thanks for the reference to Julia Lawall's response to your question. There are other problems with this code, as is noted in the rule. 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. 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). Right? Coverity Scan - Static Analysis I'm sorry if I have misunderstood the intent in your question. 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. And in this step. 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 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. C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. We should Zoom if you wish to talk more. Correct; a null pointer is not a valid pointer for the C library functions. *var1 = 0; this dereferences the pointer, i.e. Markus:AFAICT the respponses to this StackOverflow question agree with my previous assertions. If the compiler finds a pointer dereference, it treats that pointer as nonnull. Ah, gotcha. accesses memory stored at its address. Generating points along line with specifying the origin of point generation in QGIS. IMHO, the rule title should be changed to something less general. Synopsys, Inc. | Policy Statement | Contact. 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. What is it that I did not understand? Is there a generic term for these trajectories? rev2023.5.1.43405. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. NULL Pointer Dereference in mruby/mruby- vulnerability database 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 Scan - Static Analysis It would have been terrible to A simple decrement that wraps around causing an array overflow on lsm->lsm_oinfo[i[. 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. 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. However, the warning has value because it is pointing [sic] out that the safety of q is not trivially obvious from your function's logic. Carnegie Mellon University Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. Coverity Scan - Static Analysis 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! Many platforms can support testing for those also. CPE Name Name Version; mruby: 3.1.0: Products. 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. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy(). There are only two condidtions in my code, cond1 and cond2. Can corresponding author withdraw a paper after it has accepted without permission/acceptance of first author. Why does Acts not mention the deaths of Peter and Paul? WG21 (the C++ working group) may wish to define 0->y, and they are within their right to do so. 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. So no checking of the length is necessary (besides preventing integer overflow, which the compliant solution does). This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. It worked normally, but sometimes devices had cryptic types. This compliant solution eliminates the null pointer deference by initializing sk to tun->sk following the null pointer check. Thanks for contributing an answer to Stack Overflow! Thanks for contributing an answer to Stack Overflow! What should I follow, if two altimeters show different altitudes? Solution 1, it looks like, today's solution tomorrow's problem. {"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. 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). Example: tool developers, security researchers, pen-testers, incident response analysts. Finally, there is the matter of the compliant solution. Pointer members in structs are not checked. Alternate Terms Relationships The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. If you want to change the value of your pointer, just do. At this point we define size as strlen(input_str) + 1. To learn more, see our tips on writing great answers. Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage. Possible Null Pointer exception was found in a feature in which I'm the feature owner. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). It evaluates to true if a_ptr is not NULL. void host_lookup(char *user_supplied_addr){, if("com.example.URLHandler.openURL".equals(intent.getAction())) {. Would you become interested in a related clarification approach for a discussion topic like . 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. I'll add that right now, but I feel it's pointless, since it will only clutter up the question. Would such an aspect be influenced in any ways if the address of operator would be applied around similar expressions? On many platforms, dereferencing a null pointer results inabnormal program termination, but this is not required by the standard. 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? It was causing glusterd daemon crash for glusterfs. Note that this code is also vulnerable to a buffer overflow (CWE-119). Finding the distance from a corner of a cube to the midpoint of an edge. Is there any known 80-bit collision attack? Best to cite C11 s7.24.2.1 here: The memcpy function copies n characters from the object pointed to by s2 into the object pointed to by s1. How do the interferometers on the drag-free satellite LISA receive power without altering their geodesic trajectory? You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. of making the mruby interpreter crash, thus affecting the. 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. And Coverity will tend to interpret your code rather than reading your mind. (I think you cover that in a different rule.) User without create permission can create a custom object from Managed package using Custom Rest API. Will the ordering matter a bit more for the safe evaluation of involved expressions? Null reference creation and null pointer dereference 2012-09-11. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. What were the most popular text editors for MS-DOS in the 1980s? 2019-07-15. Coverity is correctly telling you that, albeit in a somewhat indirect way. Expressions (EXP), Weaknesses in the 2019 CWE Top 25 Most Dangerous Software Errors, Weaknesses in the 2021 CWE Top 25 Most Dangerous Software Weaknesses, Weaknesses in the 2020 CWE Top 25 Most Dangerous Software Weaknesses, Weaknesses in the 2022 CWE Top 25 Most Dangerous Software Weaknesses, Comprehensive Categorization: Poor Coding Practices, https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf, https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf, https://en.wikipedia.org/wiki/Null_pointer#Null_dereferencing, https://developer.apple.com/documentation/xcode/null-reference-creation-and-null-pointer-dereference, https://www.immuniweb.com/vulnerability/null-pointer-dereference.html, Cybersecurity and Infrastructure Security Agency, Homeland Security Systems Engineering and Development Institute, Null Dereference (Null Pointer Dereference), updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities, updated Common_Consequences, Demonstrative_Examples, Other_Notes, Potential_Mitigations, Weakness_Ordinalities, updated Potential_Mitigations, Relationships, updated Demonstrative_Examples, Description, Detection_Factors, Potential_Mitigations, updated Demonstrative_Examples, Observed_Examples, Relationships, updated Related_Attack_Patterns, Relationships, updated Observed_Examples, Related_Attack_Patterns, Relationships, updated Relationships, Taxonomy_Mappings, White_Box_Definitions, updated Demonstrative_Examples, Observed_Examples, updated Alternate_Terms, Applicable_Platforms, Observed_Examples, updated Demonstrative_Examples, Detection_Factors, References, Relationships. It does not give the pointer a new value. This table shows the weaknesses and high level categories that are related to this weakness. How a top-ranked engineering school reimagined CS curriculum (Ep. 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?). <. This one is pretty awesome. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Your assertion is not backed by the wording in the standard, nor by common implementer understanding. I see coverity defect with bold/italic code. Even if that memory contains a pointer which is not valid, or has been freed. 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. Not the answer you're looking for? Apple. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); Image of minimal degree representation of quasisimple group unique up to conjugacy. Coverity - forward null dereference #1747 - Github Does &((struct name *)NULL -> b) cause undefined behaviour in C11? Fixed by setting name to Oh joy. Shouldn't the function check all pointers before dereferencing them or passing them to another function? If it wasn't for coverity Resource leaks: I hate them, especially in libc, which is code you expect to be hot. Our code base contains a lot of copy paste mistakes, we are glad that there is a tool like coverity that can help to detect them. In the case of the ARM and XScale architectures, the 0x0 address is mapped in memory and serves as the exception vector table; consequently, dereferencing 0x0 did not cause an abnormal program termination. How to force Unity Editor/TestRunner to run at full speed when in background? Base - a weakness Not the answer you're looking for? What is it that I did not understand? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy.

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