From: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Subject: userfaultfd: selftests: fix SIGSEGV if huge mmap fails The error handling in hugetlb_allocate_area() was incorrect for the hugetlb_shared test case. Previously the behavior was: - mmap a hugetlb area - If this fails, set the pointer to NULL, and carry on - mmap an alias of the same hugetlb fd - If this fails, munmap the original area If the original mmap failed, it's likely the second one did too. If both failed, we'd blindly try to munmap a NULL pointer, causing a SIGSEGV. Instead, "goto fail" so we return before trying to mmap the alias. This issue can be hit "in real life" by forgetting to set /proc/sys/vm/nr_hugepages (leaving it at 0), and then trying to run the hugetlb_shared test. Another small improvement is, when the original mmap fails, don't just print "it failed": perror(), so we can see *why*. :) Link: https://lkml.kernel.org/r/20201204203443.2714693-1-axelrasmussen@xxxxxxxxxx Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: Shuah Khan <shuah@xxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Joe Perches <joe@xxxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: David Alan Gilbert <dgilbert@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- tools/testing/selftests/vm/userfaultfd.c | 25 +++++++++++++-------- 1 file changed, 16 insertions(+), 9 deletions(-) --- a/tools/testing/selftests/vm/userfaultfd.c~userfaultfd-selftests-fix-sigsegv-if-huge-mmap-fails +++ a/tools/testing/selftests/vm/userfaultfd.c @@ -206,19 +206,19 @@ static int hugetlb_release_pages(char *r return ret; } - static void hugetlb_allocate_area(void **alloc_area) { void *area_alias = NULL; char **alloc_area_alias; + *alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE, (map_shared ? MAP_SHARED : MAP_PRIVATE) | MAP_HUGETLB, huge_fd, *alloc_area == area_src ? 0 : nr_pages * page_size); if (*alloc_area == MAP_FAILED) { - fprintf(stderr, "mmap of hugetlbfs file failed\n"); - *alloc_area = NULL; + perror("mmap of hugetlbfs file failed"); + goto fail; } if (map_shared) { @@ -227,14 +227,11 @@ static void hugetlb_allocate_area(void * huge_fd, *alloc_area == area_src ? 0 : nr_pages * page_size); if (area_alias == MAP_FAILED) { - if (munmap(*alloc_area, nr_pages * page_size) < 0) { - perror("hugetlb munmap"); - exit(1); - } - *alloc_area = NULL; - return; + perror("mmap of hugetlb file alias failed"); + goto fail_munmap; } } + if (*alloc_area == area_src) { huge_fd_off0 = *alloc_area; alloc_area_alias = &area_src_alias; @@ -243,6 +240,16 @@ static void hugetlb_allocate_area(void * } if (area_alias) *alloc_area_alias = area_alias; + + return; + +fail_munmap: + if (munmap(*alloc_area, nr_pages * page_size) < 0) { + perror("hugetlb munmap"); + exit(1); + } +fail: + *alloc_area = NULL; } static void hugetlb_alias_mapping(__u64 *start, size_t len, unsigned long offset) _
