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ceph: fix race in concurrent __ceph_remove_cap invocations

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commit e5cafce3ad0f8652d6849314d951459c2bff7233 upstream.

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. Those callers hold the session->s_mutex, so they
are prevented from concurrent execution, but ceph_evict_inode does not.

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.

Cc: [email protected]
URL: https://tracker.ceph.com/issues/43272
Suggested-by: Jeff Layton <[email protected]>
Signed-off-by: Luis Henriques <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Luis Henriques 2020-11-12 10:45:12 +00:00 • committed by Greg Kroah-Hartman
commit f22f743a2a
1 changed files with 9 additions and 2 deletions
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11
fs/ceph/caps.c
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@ -1052,12 +1052,19 @@ 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 the 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)