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exec: Use sane stack rlimit under secureexec

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For a secureexec, before memory layout selection has happened, reset the
stack rlimit to something sane to avoid the caller having control over
the resulting layouts.

$ ulimit -s
8192
$ ulimit -s unlimited
$ /bin/sh -c 'ulimit -s'
unlimited
$ sudo /bin/sh -c 'ulimit -s'
8192

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: James Morris <james.l.morris@oracle.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
This commit is contained in:
Kees Cook 2017-07-18 15:25:35 -07:00
parent 473d89639d
commit 64701dee41
1 changed files with 12 additions and 0 deletions
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12
fs/exec.c
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@ -1350,6 +1350,18 @@ void setup_new_exec(struct linux_binprm * bprm)
*/ */
bprm->secureexec |= bprm->cap_elevated; bprm->secureexec |= bprm->cap_elevated;
if (bprm->secureexec) {
/*
* For secureexec, reset the stack limit to sane default to
* 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.
*/
if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM)
current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM;
}
arch_pick_mmap_layout(current->mm); arch_pick_mmap_layout(current->mm);
current->sas_ss_sp = current->sas_ss_size = 0; current->sas_ss_sp = current->sas_ss_size = 0;