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Subject[PATCH] ceph: fix race in concurrent __ceph_remove_cap invocations
Date
A NULL pointer dereference may occur in __ceph_remove_cap with some of the
callbacks used in ceph_iterate_session_caps, namely trim_caps_cb and
remove_session_caps_cb. These aren't protected against the concurrent
execution of __ceph_remove_cap.

Since the callers of this function hold the i_ceph_lock, the fix is simply
a matter of returning immediately if caps->ci is NULL.

Based on a patch from Jeff Layton.

Cc: stable@vger.kernel.org
URL: https://tracker.ceph.com/issues/43272
Link: https://www.spinics.net/lists/ceph-devel/msg47064.html
Signed-off-by: Luis Henriques <lhenriques@suse.de>
---
fs/ceph/caps.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index ded4229c314a..443f164760d5 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1140,12 +1140,19 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release)
{
struct ceph_mds_session *session = cap->session;
struct ceph_inode_info *ci = cap->ci;
- struct ceph_mds_client *mdsc =
- ceph_sb_to_client(ci->vfs_inode.i_sb)->mdsc;
+ struct ceph_mds_client *mdsc;
int removed = 0;

+ /* 'ci' being NULL means he remove have already occurred */
+ if (!ci) {
+ dout("%s: cap inode is NULL\n", __func__);
+ return;
+ }
+
dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode);

+ mdsc = ceph_inode_to_client(&ci->vfs_inode)->mdsc;
+
/* remove from inode's cap rbtree, and clear auth cap */
rb_erase(&cap->ci_node, &ci->i_caps);
if (ci->i_auth_cap == cap) {
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