linux-kernel - [PATCH] Revert "exec: avoid RLIMIT

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Date:   Tue, 12 Dec 2017 11:28:38 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Laura Abbott <labbott@...hat.com>,
        Tomáš Trnka <trnka@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Revert "exec: avoid RLIMIT_STACK races with prlimit()"

This reverts commit 04e35f4495dd560db30c25efca4eecae8ec8c375.

SELinux runs with secureexec for all non-"noatsecure" domain transitions,
which means lots of processes end up hitting the stack hard-limit change
that was introduced in order to fix a race with prlimit(). That race fix
will need to be redesigned.

Reported-by: Laura Abbott <labbott@...hat.com>
Reported-by: Tomáš Trnka <trnka@....com>
Cc: stable@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/exec.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 6be2aa0ab26f..1d6243d9f2b6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1340,15 +1340,10 @@ 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
-		 * races from other threads changing the limits. This also
-		 * must be protected from races with prlimit() calls.
+		 * needing to clean up the change on failure.
 		 */
-		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