From df29db0bec24211cfc917db52024bf8deecac2c9 Mon Sep 17 00:00:00 2001 From: Mike Frysinger Date: Wed, 15 Mar 2017 23:59:31 -0700 Subject: posix_spawn: use a larger min stack for -fstack-check [BZ #21253] When glibc is built with -fstack-check, trying to use posix_spawn can lead to segfaults due to gcc internally probing stack memory too far. The new spawn API will allocate a minimum of 1 page, but the stack checking logic might probe a couple of pages. When it tries to walk them, everything falls apart. The gcc internal docs [1] state the default interval checking is one page. Which means we need two pages (the current one, and the next probed). No target currently defines it larger. Further, it mentions that the default minimum stack size needed to recover from an overflow is 4/8KiB for sjlj or 8/12KiB for others. But some Linux targets (like mips and ppc) go up to 16KiB (and some non-Linux targets go up to 24KiB). Let's create each child with a minimum of 32KiB slack space to support them all, and give us future breathing room. No test is added as existing ones crash. Even a simple call is enough to trigger the problem: char *argv[] = { "/bin/ls", NULL }; posix_spawn(NULL, "/bin/ls", NULL, NULL, argv, NULL); [1] https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gccint/Stack-Checking.html (cherry picked from commit 21f042c804835d1f7a4a8e06f2c93ca35a182042) diff --git a/ChangeLog b/ChangeLog index 321bf53191..b37a054bae 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2017-04-03 Mike Frysinger + + [BZ #21253] + * sysdeps/unix/sysv/linux/spawni.c (__spawnix): Increase argv_size + slack space by 32KiB. + 2017-04-03 Wladimir van der Laan [BZ# 21338] diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c index c96aac889d..29d8f25ab5 100644 --- a/sysdeps/unix/sysv/linux/spawni.c +++ b/sysdeps/unix/sysv/linux/spawni.c @@ -319,6 +319,11 @@ __spawnix (pid_t * pid, const char *file, /* Add a slack area for child's stack. */ size_t argv_size = (argc * sizeof (void *)) + 512; + /* We need at least a few pages in case the compiler's stack checking is + enabled. In some configs, it is known to use at least 24KiB. We use + 32KiB to be "safe" from anything the compiler might do. Besides, the + extra pages won't actually be allocated unless they get used. */ + argv_size += (32 * 1024); size_t stack_size = ALIGN_UP (argv_size, GLRO(dl_pagesize)); void *stack = __mmap (NULL, stack_size, prot, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0); -- 2.13.1