3.16.80-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Luis Henriques lhenriques@suse.com
commit ea60ed6fcf29eebc78f2ce91491e6309ee005a01 upstream.
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.
Signed-off-by: Luis Henriques lhenriques@suse.com Reviewed-by: Jeff Layton jlayton@kernel.org Signed-off-by: Ilya Dryomov idryomov@gmail.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/ceph/caps.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
--- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -913,6 +913,11 @@ void __ceph_remove_cap(struct ceph_cap *
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); /* @@ -939,11 +944,6 @@ void __ceph_remove_cap(struct ceph_cap * cap->ci = NULL; 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);