From 7be77e20d59fc3dd3fdde31641e0bc821114d26b Mon Sep 17 00:00:00 2001 From: Pavel Emelianov Date: Tue, 31 Jul 2007 00:38:48 -0700 Subject: [PATCH] Fix user struct leakage with locked IPC shem segment When user locks an ipc shmem segmant with SHM_LOCK ctl and the segment is already locked the shmem_lock() function returns 0. After this the subsequent code leaks the existing user struct: == ipc/shm.c: sys_shmctl() == ... err = shmem_lock(shp->shm_file, 1, user); if (!err) { shp->shm_perm.mode |= SHM_LOCKED; shp->mlock_user = user; } ... == Other results of this are: 1. the new shp->mlock_user is not get-ed and will point to freed memory when the task dies. 2. the RLIMIT_MEMLOCK is screwed on both user structs. The exploit looks like this: == id = shmget(...); setresuid(uid, 0, 0); shmctl(id, SHM_LOCK, NULL); setresuid(uid + 1, 0, 0); shmctl(id, SHM_LOCK, NULL); == My solution is to return 0 to the userspace and do not change the segment's user. Signed-off-by: Pavel Emelianov Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/shm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/ipc/shm.c b/ipc/shm.c index d88ac5a07ec7..a86a3a5c8a19 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -716,7 +716,7 @@ asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds __user *buf) struct user_struct * user = current->user; if (!is_file_hugepages(shp->shm_file)) { err = shmem_lock(shp->shm_file, 1, user); - if (!err) { + if (!err && !(shp->shm_perm.mode & SHM_LOCKED)){ shp->shm_perm.mode |= SHM_LOCKED; shp->mlock_user = user; } -- GitLab