From: Xiubo Li <xiubo.li@clyso.com> mainline inclusion from mainline-v7.3-rc1 commit 7af4c4f01305b0935adf6d4301b1ec407025485d category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/19017 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- list_for_each_entry() iterates ci->i_cap_flush_list but drops i_ceph_lock to send cap messages. During the unlock window, handle_cap_flush_ack() can acquire i_ceph_lock, detach cf entries with tid <= flush_tid from the list, release i_ceph_lock, and free them via ceph_free_cap_flush() outside any lock. When the original thread reacquires i_ceph_lock and the for-loop macro advances via cf = list_next_entry(cf, i_list), it dereferences cf->i_list.next on freed memory. The race timeline: __kick_flushing_caps() handle_cap_flush_ack() ----------------------- ----------------------- holds i_ceph_lock <--- iterates to cf (tid=10) prepares FLUSH message drops i_ceph_lock <--- __send_cap() ── FLUSH(tid=10) MDS sends FLUSH_ACK(tid=10) ---> acquires i_ceph_lock cf->tid(10) <= flush_tid(10), detaches cf from i_cap_flush_list drops i_ceph_lock ceph_free_cap_flush(cf) <- frees it! acquires i_ceph_lock <--- for-loop advances: cf = list_next_entry(cf, i_list) -- UAF on freed cf->i_list.next The cf was just sent by __kick_flushing_caps itself via __send_cap(). The MDS may respond with FLUSH_ACK quickly enough that handle_cap_flush_ack() frees cf before __kick_flushing_caps can finish the iteration. Fix by converting to a manual while loop: save the next pointer under i_ceph_lock before dropping it, then use the saved pointer after reacquiring, so the potentially-freed cf is never accessed again. Cc: stable@vger.kernel.org Signed-off-by: Xiubo Li <xiubo.li@clyso.com> Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com> Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Chen Yuxi <chenyuxi19@huawei.com> --- 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 9bebdafd5ec9..d709edea84ae 100644 --- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -2513,9 +2513,14 @@ static void __kick_flushing_caps(struct ceph_mds_client *mdsc, } } - list_for_each_entry(cf, &ci->i_cap_flush_list, i_list) { - if (cf->tid < first_tid) + cf = list_first_entry(&ci->i_cap_flush_list, struct ceph_cap_flush, i_list); + while (&cf->i_list != &ci->i_cap_flush_list) { + struct ceph_cap_flush *next; + + if (cf->tid < first_tid) { + cf = list_next_entry(cf, i_list); continue; + } cap = ci->i_auth_cap; if (!(cap && cap->session == session)) { @@ -2525,6 +2530,7 @@ static void __kick_flushing_caps(struct ceph_mds_client *mdsc, } first_tid = cf->tid + 1; + next = list_next_entry(cf, i_list); if (!cf->is_capsnap) { struct cap_msg_args arg; @@ -2565,6 +2571,7 @@ static void __kick_flushing_caps(struct ceph_mds_client *mdsc, } spin_lock(&ci->i_ceph_lock); + cf = next; } } -- 2.34.1