diff options
author | Greg Thelen | 2013-11-21 14:32:00 -0800 |
---|---|---|
committer | Linus Torvalds | 2013-11-21 16:42:27 -0800 |
commit | a399b29dfbaaaf91162b2dc5a5875dd51bbfa2a1 (patch) | |
tree | dfff401b36b593b284cd21e4051ad7a23a944845 /ipc/shm.c | |
parent | 30b0a105d9f7141e4cbf72ae5511832457d89788 (diff) |
ipc,shm: fix shm_file deletion races
When IPC_RMID races with other shm operations there's potential for
use-after-free of the shm object's associated file (shm_file).
Here's the race before this patch:
TASK 1 TASK 2
------ ------
shm_rmid()
ipc_lock_object()
shmctl()
shp = shm_obtain_object_check()
shm_destroy()
shum_unlock()
fput(shp->shm_file)
ipc_lock_object()
shmem_lock(shp->shm_file)
<OOPS>
The oops is caused because shm_destroy() calls fput() after dropping the
ipc_lock. fput() clears the file's f_inode, f_path.dentry, and
f_path.mnt, which causes various NULL pointer references in task 2. I
reliably see the oops in task 2 if with shmlock, shmu
This patch fixes the races by:
1) set shm_file=NULL in shm_destroy() while holding ipc_object_lock().
2) modify at risk operations to check shm_file while holding
ipc_object_lock().
Example workloads, which each trigger oops...
Workload 1:
while true; do
id=$(shmget 1 4096)
shm_rmid $id &
shmlock $id &
wait
done
The oops stack shows accessing NULL f_inode due to racing fput:
_raw_spin_lock
shmem_lock
SyS_shmctl
Workload 2:
while true; do
id=$(shmget 1 4096)
shmat $id 4096 &
shm_rmid $id &
wait
done
The oops stack is similar to workload 1 due to NULL f_inode:
touch_atime
shmem_mmap
shm_mmap
mmap_region
do_mmap_pgoff
do_shmat
SyS_shmat
Workload 3:
while true; do
id=$(shmget 1 4096)
shmlock $id
shm_rmid $id &
shmunlock $id &
wait
done
The oops stack shows second fput tripping on an NULL f_inode. The
first fput() completed via from shm_destroy(), but a racing thread did
a get_file() and queued this fput():
locks_remove_flock
__fput
____fput
task_work_run
do_notify_resume
int_signal
Fixes: c2c737a0461e ("ipc,shm: shorten critical region for shmat")
Fixes: 2caacaa82a51 ("ipc,shm: shorten critical region for shmctl")
Signed-off-by: Greg Thelen <gthelen@google.com>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: <stable@vger.kernel.org> # 3.10.17+ 3.11.6+
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc/shm.c')
-rw-r--r-- | ipc/shm.c | 28 |
1 files changed, 23 insertions, 5 deletions
diff --git a/ipc/shm.c b/ipc/shm.c index d69739610fd4..0bdf21c6814e 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -208,15 +208,18 @@ static void shm_open(struct vm_area_struct *vma) */ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp) { + struct file *shm_file; + + shm_file = shp->shm_file; + shp->shm_file = NULL; ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT; shm_rmid(ns, shp); shm_unlock(shp); - if (!is_file_hugepages(shp->shm_file)) - shmem_lock(shp->shm_file, 0, shp->mlock_user); + if (!is_file_hugepages(shm_file)) + shmem_lock(shm_file, 0, shp->mlock_user); else if (shp->mlock_user) - user_shm_unlock(file_inode(shp->shm_file)->i_size, - shp->mlock_user); - fput (shp->shm_file); + user_shm_unlock(file_inode(shm_file)->i_size, shp->mlock_user); + fput(shm_file); ipc_rcu_putref(shp, shm_rcu_free); } @@ -983,6 +986,13 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf) } shm_file = shp->shm_file; + + /* check if shm_destroy() is tearing down shp */ + if (shm_file == NULL) { + err = -EIDRM; + goto out_unlock0; + } + if (is_file_hugepages(shm_file)) goto out_unlock0; @@ -1101,6 +1111,14 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr, goto out_unlock; ipc_lock_object(&shp->shm_perm); + + /* check if shm_destroy() is tearing down shp */ + if (shp->shm_file == NULL) { + ipc_unlock_object(&shp->shm_perm); + err = -EIDRM; + goto out_unlock; + } + path = shp->shm_file->f_path; path_get(&path); shp->shm_nattch++; |