From: Chris Gellermann Date: Wed, 22 Jul 2026 13:02:45 +0000 (+0200) Subject: selftests/clone3: fix wild pointer access of getline due to missing init X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8f6f9fd93cd7a5dd607ad5cd910476dd68fff3ed;p=thirdparty%2Flinux.git selftests/clone3: fix wild pointer access of getline due to missing init Patch series "selftests: Add missing initalization of pointer passed to getline", v2. This patch (of 2): Clone3_set_tid uses getline(&line, ...) in a loop to read the child's process status. The code expects that getline allocates the buffer for the line on the first loop iteration. According to the Open Group Spec[1], char *line has to be null pointer for this: > ssize_t getline(char **restrict lineptr, ...); > If *lineptr is a null pointer or if the object pointed to by *lineptr > is of insufficient size, an object shall be allocated as if by malloc() > or the object shall be reallocated as if by realloc()[...]. However, char *line is only declared, leading to an undefined value that is potentially non-null. In an example run with Musl v1.2.6, the realloc call[2] of getdelim, which implements getline, triggers a segfault: ./run_kselftest.sh --test clone3:clone3_set_tid [ 1366.165898] kselftest: Running tests in clone3 ... [ 1367.799244] clone3_set_tid[811]: unhandled signal 11 code 0x1 at 0x0000000000000000 in libc.so[68184,3fbf69f000+4c000] [ 1367.802808] CPU: 0 UID: 0 PID: 811 Comm: clone3_set_tid Not tainted .. [ 1367.804188] epc: 0x0000003fbf6b0184 [ 1367.804188] ra : 0x0000003fbf6d4664 [ 1367.804188] sp : 0x0000003fce5f2e40 [ 1367.805314] gp : 0x0000002aaab0dfb8 [ 1367.805314] tp : 0x0000003fbf6f14a8 [ 1367.805314] t0 : 0x0000003fbf63d000 ... Looking at the realloc implementation, Musl mallocs for a null pointer memory. But for a non-null pointer, it assumes it's passed a valid pointer to the heap and tries to access its meta-data. This leads to the segfault we see: void *realloc(void *p, size_t n) { if (!p) return malloc(n); if (size_overflows(n)) return 0; struct meta *g = get_meta(p); ... } Fix this by properly initializing the line pointer to NULL. Link: https://lore.kernel.org/20260722130246.2135563-1-christian.gellermann@codasip.com Link: https://lore.kernel.org/20260722130246.2135563-2-christian.gellermann@codasip.com Link: https://pubs.opengroup.org/onlinepubs/9799919799/functions/getline.html [1] Link: https://git.musl-libc.org/cgit/musl/tree/src/stdio/getdelim.c#n38 [2] Fixes: 41585bbeeef9 ("selftests: add tests for clone3() with *set_tid") Signed-off-by: Chris Gellermann Acked-by: David Hildenbrand (arm) Reviewed-by: Lorenzo Stoakes Cc: Christian Brauner Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton --- diff --git a/tools/testing/selftests/clone3/clone3_set_tid.c b/tools/testing/selftests/clone3/clone3_set_tid.c index 5c944aee6b41..485efa7c9eed 100644 --- a/tools/testing/selftests/clone3/clone3_set_tid.c +++ b/tools/testing/selftests/clone3/clone3_set_tid.c @@ -141,7 +141,7 @@ int main(int argc, char *argv[]) { FILE *f; char buf; - char *line; + char *line = NULL; int status; int ret = -1; size_t len = 0;