While the defense-in-depth RLIMIT_STACK limit on setuid processes was protected against races from other threads calling setrlimit(), I missed protecting it against races from external processes calling prlimit(). This adds locking around the change and makes sure that rlim_max is set too.
Reported-by: Ben Hutchings <[email protected]> Reported-by: Brad Spengler <[email protected]> Fixes: 64701dee4178e ("exec: Use sane stack rlimit under secureexec") Cc: [email protected] Cc: James Morris <[email protected]> Cc: Serge Hallyn <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Jiri Slaby <[email protected]> Signed-off-by: Kees Cook <[email protected]> --- fs/exec.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/exec.c b/fs/exec.c index 1d6243d9f2b6..6be2aa0ab26f 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1340,10 +1340,15 @@ void setup_new_exec(struct linux_binprm * bprm) * avoid bad behavior from the prior rlimits. This has to * happen before arch_pick_mmap_layout(), which examines * RLIMIT_STACK, but after the point of no return to avoid - * needing to clean up the change on failure. + * races from other threads changing the limits. This also + * must be protected from races with prlimit() calls. */ + task_lock(current->group_leader); if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM) current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM; + if (current->signal->rlim[RLIMIT_STACK].rlim_max > _STK_LIM) + current->signal->rlim[RLIMIT_STACK].rlim_max = _STK_LIM; + task_unlock(current->group_leader); } arch_pick_mmap_layout(current->mm); -- 2.7.4 -- Kees Cook Pixel Security
