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Subject[PATCH v5 14/15] exec: Use sane stack rlimit under secureexec
Date
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>
---
fs/exec.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index 3006c1c24304..3235cbd85efa 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1350,6 +1350,18 @@ void setup_new_exec(struct linux_binprm * bprm)
*/
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);

current->sas_ss_sp = current->sas_ss_size = 0;
--
2.7.4
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