#include <stdio.h> #include <stdlib.h> #include <stdint.h> int main(void) { void *f = malloc(SIZE_MAX); if(!f) return 1; free(f); return 0; } If you compile any code that uses *alloc functions with -fno-builtin or -fno-builtin-malloc you will not get useful warnings from GCC like c.c:11:15: warning: argument 1 value ‘18446744073709551615’ exceeds maximum object size 9223372036854775807 [-Walloc-size-larger-than=] This happens because stdlib.h / malloc.h lacks of __attribute_alloc_size__ annocations for functions malloc, calloc, realloc, reallocarray.
It has been discussed how to handle objects larger than PTRDIFF_MAX on GCC PR#67999 [1] and I think the issue is now glibc *does* allow such objects. We do use on C11 aligned_alloc, but my guess is to enforce size is multiple than alignment instead of enforcing object size are no larger than PTRDIFF_MAX. It seems that some *very* specific programs does allocate objects larger PTRDIFF_MAX, as indicated by Florian in GCC PR, but I also see that current GCC support for such objects is sketchy to say at least and others libc are moving to not allow it. So I think before adding such annotation we need discuss whether we want to allow such kind of allocation on malloc and mmap functions. I will bring this on discussion at libc-alpha. [1] https://gcc.gnu.org/bugzilla//show_bug.cgi?id=67999
The master branch has been updated by Adhemerval Zanella <azanella@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9bf8e29ca136094f73f69f725f15c51facc97206 commit 9bf8e29ca136094f73f69f725f15c51facc97206 Author: Adhemerval Zanella <adhemerval.zanella@linaro.org> Date: Tue Dec 18 16:30:56 2018 -0200 malloc: make malloc fail with requests larger than PTRDIFF_MAX (BZ#23741) As discussed previously on libc-alpha [1], this patch follows up the idea and add both the __attribute_alloc_size__ on malloc functions (malloc, calloc, realloc, reallocarray, valloc, pvalloc, and memalign) and limit maximum requested allocation size to up PTRDIFF_MAX (taking into consideration internal padding and alignment). This aligns glibc with gcc expected size defined by default warning -Walloc-size-larger-than value which warns for allocation larger than PTRDIFF_MAX. It also aligns with gcc expectation regarding libc and expected size, such as described in PR#67999 [2] and previously discussed ISO C11 issues [3] on libc-alpha. From the RFC thread [4] and previous discussion, it seems that consensus is only to limit such requested size for malloc functions, not the system allocation one (mmap, sbrk, etc.). The implementation changes checked_request2size to check for both overflow and maximum object size up to PTRDIFF_MAX. No additional checks are done on sysmalloc, so it can still issue mmap with values larger than PTRDIFF_T depending on the requested size. The __attribute_alloc_size__ is for functions that return a pointer only, which means it cannot be applied to posix_memalign (see remarks in GCC PR#87683 [5]). The runtimes checks to limit maximum requested allocation size does applies to posix_memalign. Checked on x86_64-linux-gnu and i686-linux-gnu. [1] https://sourceware.org/ml/libc-alpha/2018-11/msg00223.html [2] https://gcc.gnu.org/bugzilla//show_bug.cgi?id=67999 [3] https://sourceware.org/ml/libc-alpha/2011-12/msg00066.html [4] https://sourceware.org/ml/libc-alpha/2018-11/msg00224.html [5] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87683 [BZ #23741] * malloc/hooks.c (malloc_check, realloc_check): Use __builtin_add_overflow on overflow check and adapt to checked_request2size change. * malloc/malloc.c (__libc_malloc, __libc_realloc, _mid_memalign, __libc_pvalloc, __libc_calloc, _int_memalign): Limit maximum allocation size to PTRDIFF_MAX. (REQUEST_OUT_OF_RANGE): Remove macro. (checked_request2size): Change to inline function and limit maximum requested size to PTRDIFF_MAX. (__libc_malloc, __libc_realloc, _int_malloc, _int_memalign): Limit maximum allocation size to PTRDIFF_MAX. (_mid_memalign): Use _int_memalign call for overflow check. (__libc_pvalloc): Use __builtin_add_overflow on overflow check. (__libc_calloc): Use __builtin_mul_overflow for overflow check and limit maximum requested size to PTRDIFF_MAX. * malloc/malloc.h (malloc, calloc, realloc, reallocarray, memalign, valloc, pvalloc): Add __attribute_alloc_size__. * stdlib/stdlib.h (malloc, realloc, reallocarray, valloc): Likewise. * malloc/tst-malloc-too-large.c (do_test): Add check for allocation larger than PTRDIFF_MAX. * malloc/tst-memalign.c (do_test): Disable -Walloc-size-larger-than= around tests of malloc with negative sizes. * malloc/tst-posix_memalign.c (do_test): Likewise. * malloc/tst-pvalloc.c (do_test): Likewise. * malloc/tst-valloc.c (do_test): Likewise. * malloc/tst-reallocarray.c (do_test): Replace call to reallocarray with resulting size allocation larger than PTRDIFF_MAX with reallocarray_nowarn. (reallocarray_nowarn): New function. * NEWS: Mention the malloc function semantic change.
Fixed on 2.30 (commit 9bf8e29ca136094f73f69f725f15c51facc97206).
As previous comment.