cfids_laundromat_worker() bumps tcon->tc_count for every expired open cfid and queues cached_dir_offload_close() without checking whether the tcon is already being torn down. Racing with the final cifs_put_tcon(), the tcon comes back from zero and gets torn down twice: T1 T2 cifs_put_tcon() --tc_count == 0, TID_EXITING tconInfoFree() free_cached_dirs() cancel_delayed_work_sync() cfids_laundromat_worker() ++tc_count == 1 queue_work(serverclose_wq) kfree(tcon->origin_fullpath) kfree(tcon) cached_dir_offload_close() close_cached_dir() [UAF] cifs_put_tcon() tconInfoFree() [double free] cached_dir_lease_break() also bumps tc_count without tc_lock, racing with the laundromat's locked update. Take the tcon reference through a helper that refuses once the tcon is TID_EXITING or its refcount has dropped to zero. Queued put_work and close_work then always hold a tcon reference, so tconInfoFree() can't run before they finish and free_cached_dirs() doesn't need to flush any workqueue. If the laundromat can't get a reference, put the cfid back on the dying list for free_cached_dirs() to free; its handle goes away with the tree connection. The lease break path finds the tcon on ses->tcon_list under cifs_tcp_ses_lock, so it can't see TID_EXITING, but it now takes tc_lock. Fixes: 3fa640d035e5 ("smb: During unmount, ensure all cached dir instances drop their dentry") Signed-off-by: Paulo Alcantara Cc: David Howells Cc: Namjae Jeon Cc: Ronnie Sahlberg Cc: Shyam Prasad N Cc: Tom Talpey Cc: Bharath SM Cc: stable@vger.kernel.org --- fs/smb/client/cached_dir.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-) diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c index 647fa26da4d2..50217f47a0ed 100644 --- a/fs/smb/client/cached_dir.c +++ b/fs/smb/client/cached_dir.c @@ -649,6 +649,17 @@ void invalidate_all_cached_dirs(struct cifs_tcon *tcon, bool sync) flush_delayed_work(&cfids->laundromat_work); } +static bool cached_dir_get_tcon(struct cifs_tcon *tcon, + enum smb3_tcon_ref_trace trace) +{ + guard(spinlock)(&tcon->tc_lock); + if (tcon->status == TID_EXITING || tcon->tc_count <= 0) + return false; + ++tcon->tc_count; + trace_smb3_tcon_ref(tcon->debug_id, tcon->tc_count, trace); + return true; +} + static void cached_dir_offload_close(struct work_struct *work) { @@ -693,6 +704,9 @@ bool cached_dir_lease_break(struct cifs_tcon *tcon, __u8 lease_key[16]) !memcmp(lease_key, cfid->fid.lease_key, SMB2_LEASE_KEY_SIZE)) { + if (!cached_dir_get_tcon(tcon, + netfs_trace_tcon_ref_get_cached_lease_break)) + break; cfid->has_lease = false; cfid->time = 0; /* @@ -703,9 +717,6 @@ bool cached_dir_lease_break(struct cifs_tcon *tcon, __u8 lease_key[16]) cfid->on_list = false; cfids->num_entries--; - ++tcon->tc_count; - trace_smb3_tcon_ref(tcon->debug_id, tcon->tc_count, - netfs_trace_tcon_ref_get_cached_lease_break); queue_work(cfid_put_wq, &cfid->put_work); spin_unlock(&cfids->cfid_list_lock); return true; @@ -813,12 +824,13 @@ static void cfids_laundromat_worker(struct work_struct *work) cfid->dentry = NULL; if (cfid->is_open) { - spin_lock(&cfid->tcon->tc_lock); - ++cfid->tcon->tc_count; - trace_smb3_tcon_ref(cfid->tcon->debug_id, cfid->tcon->tc_count, - netfs_trace_tcon_ref_get_cached_laundromat); - spin_unlock(&cfid->tcon->tc_lock); - queue_work(serverclose_wq, &cfid->close_work); + if (cached_dir_get_tcon(cfid->tcon, + netfs_trace_tcon_ref_get_cached_laundromat)) { + queue_work(serverclose_wq, &cfid->close_work); + continue; + } + scoped_guard(spinlock, &cfids->cfid_list_lock) + list_add_tail(&cfid->entry, &cfids->dying); } else /* * Drop the ref-count from above, either the lease-ref (if there -- 2.56.0