[PATCH v4 14/15] exec: Use sane stack rlimit under secureexec

From	Kees Cook <keescook@chromium.org>
Newsgroups	linux.kernel
Subject	[PATCH v4 14/15] exec: Use sane stack rlimit under secureexec
Date	2017-08-01 02:00 +0200
Message-ID	<u9sLn-4eo-3@gated-at.bofh.it> (permalink)
References	<u9sLn-4eo-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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>
---
 fs/exec.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index 3ae8a40c587b..cddd2a2cbc1f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1329,6 +1329,18 @@ 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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[PATCH v4 14/15] exec: Use sane stack rlimit under secureexec Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200

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