From 475c63f7829816fa2603d903225c1ad38b6efbca Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Tue, 8 Dec 2020 20:57:18 -0800 Subject: [PATCH] mm/madvise: remove racy mm ownership check Jann spotted the security hole due to race of mm ownership check. If the task is sharing the mm_struct but goes through execve() before mm_access(), it could skip process_madvise_behavior_valid check. That makes *any advice hint* to reach into the remote process. This patch removes the mm ownership check. With it, it will lose the ability that local process could give *any* advice hint with vector interface for some reason (e.g., performance). Since there is no concrete example in upstream yet, it would be better to remove the abiliity at this moment and need to review when such new advice comes up. Change-Id: I536de5167b6cf7378a06a6b7815f1dd2869a56a4 Fixes: ecb8ac8b1f14 ("mm/madvise: introduce process_madvise() syscall: an external memory hinting API") Reported-by: Jann Horn Suggested-by: Jann Horn Signed-off-by: Minchan Kim Signed-off-by: Linus Torvalds Git-Commit: a68a0262abdaa251e12c53715f48e698a18ef402 Git-Repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git Signed-off-by: Charan Teja Reddy --- mm/madvise.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index b85bfe989984..fb90ea004277 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1280,8 +1280,7 @@ SYSCALL_DEFINE6(process_madvise, int, which, pid_t, upid, goto put_pid; } - if (task->mm != current->mm && - !process_madvise_behavior_valid(behavior)) { + if (!process_madvise_behavior_valid(behavior)) { ret = -EINVAL; goto release_task; }