From: Luis Henriques <lhenriques@suse.com>
Date: Fri, 25 Oct 2019 14:05:24 +0100
Subject: ceph: fix use-after-free in __ceph_remove_cap()
Git-commit: ea60ed6fcf29eebc78f2ce91491e6309ee005a01
Patch-mainline: v5.4-rc7
References: bsc#1154058
KASAN reports a use-after-free when running xfstest generic/531, with the
following trace:
[ 293.903362] kasan_report+0xe/0x20
[ 293.903365] rb_erase+0x1f/0x790
[ 293.903370] __ceph_remove_cap+0x201/0x370
[ 293.903375] __ceph_remove_caps+0x4b/0x70
[ 293.903380] ceph_evict_inode+0x4e/0x360
[ 293.903386] evict+0x169/0x290
[ 293.903390] __dentry_kill+0x16f/0x250
[ 293.903394] dput+0x1c6/0x440
[ 293.903398] __fput+0x184/0x330
[ 293.903404] task_work_run+0xb9/0xe0
[ 293.903410] exit_to_usermode_loop+0xd3/0xe0
[ 293.903413] do_syscall_64+0x1a0/0x1c0
[ 293.903417] entry_SYSCALL_64_after_hwframe+0x44/0xa9
This happens because __ceph_remove_cap() may queue a cap release
(__ceph_queue_cap_release) which can be scheduled before that cap is
removed from the inode list with
rb_erase(&cap->ci_node, &ci->i_caps);
And, when this finally happens, the use-after-free will occur.
This can be fixed by removing the cap from the inode list before being
removed from the session list, and thus eliminating the risk of an UAF.
Cc: stable@vger.kernel.org
Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
fs/ceph/caps.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index d3b9c9d5c1bd..f5a38910a82b 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1058,6 +1058,11 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release)
dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode);
+ /* remove from inode's cap rbtree, and clear auth cap */
+ rb_erase(&cap->ci_node, &ci->i_caps);
+ if (ci->i_auth_cap == cap)
+ ci->i_auth_cap = NULL;
+
/* remove from session list */
spin_lock(&session->s_cap_lock);
if (session->s_cap_iterator == cap) {
@@ -1091,11 +1096,6 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release)
spin_unlock(&session->s_cap_lock);
- /* remove from inode list */
- rb_erase(&cap->ci_node, &ci->i_caps);
- if (ci->i_auth_cap == cap)
- ci->i_auth_cap = NULL;
-
if (removed)
ceph_put_cap(mdsc, cap);