From e79b0332ae06b4895dcecddf4bbc5d3917e9383c Mon Sep 17 00:00:00 2001 From: Aurelien Aptel Date: Tue, 7 Apr 2020 11:49:55 +0200 Subject: [PATCH] cifs: ignore cached share root handle closing errors Fix tcon use-after-free and NULL ptr deref. Customer system crashes with the following kernel log: [462233.169868] CIFS VFS: Cancelling wait for mid 4894753 cmd: 14 => a QUERY DIR [462233.228045] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4 [462233.305922] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4 [462233.306205] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4 [462233.347060] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4 [462233.347107] CIFS VFS: Close unmatched open [462233.347113] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038 ... [exception RIP: cifs_put_tcon+0xa0] (this is doing tcon->ses->server) #6 [...] smb2_cancelled_close_fid at ... [cifs] #7 [...] process_one_work at ... #8 [...] worker_thread at ... #9 [...] kthread at ... The most likely explanation we have is: * When we put the last reference of a tcon (refcount=0), we close the cached share root handle. * If closing a handle is interrupted, SMB2_close() will queue a SMB2_close() in a work thread. * The queued object keeps a tcon ref so we bump the tcon refcount, jumping from 0 to 1. * We reach the end of cifs_put_tcon(), we free the tcon object despite it now having a refcount of 1. * The queued work now runs, but the tcon, ses & server was freed in the meantime resulting in a crash. THREAD 1 ======== cifs_put_tcon => tcon refcount reach 0 SMB2_tdis close_shroot_lease close_shroot_lease_locked => if cached root has lease && refcount = 0 smb2_close_cached_fid => if cached root valid SMB2_close => retry close in a thread if interrupted smb2_handle_cancelled_close __smb2_handle_cancelled_close => !! tcon refcount bump 0 => 1 !! INIT_WORK(&cancelled->work, smb2_cancelled_close_fid); queue_work(cifsiod_wq, &cancelled->work) => queue work tconInfoFree(tcon); ==> freed! cifs_put_smb_ses(ses); ==> freed! THREAD 2 (workqueue) ======== smb2_cancelled_close_fid SMB2_close(0, cancelled->tcon, ...); => use-after-free of tcon cifs_put_tcon(cancelled->tcon); => tcon refcount reach 0 second time *CRASH* Fixes: d9191319358d ("CIFS: Close cached root handle only if it has a lease") Signed-off-by: Aurelien Aptel Signed-off-by: Steve French Reviewed-by: Pavel Shilovsky --- fs/cifs/smb2misc.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c index 0511aaf451d4..497afb0b9960 100644 --- a/fs/cifs/smb2misc.c +++ b/fs/cifs/smb2misc.c @@ -766,6 +766,20 @@ smb2_handle_cancelled_close(struct cifs_tcon *tcon, __u64 persistent_fid, cifs_dbg(FYI, "%s: tc_count=%d\n", __func__, tcon->tc_count); spin_lock(&cifs_tcp_ses_lock); + if (tcon->tc_count <= 0) { + struct TCP_Server_Info *server = NULL; + + WARN_ONCE(tcon->tc_count < 0, "tcon refcount is negative"); + spin_unlock(&cifs_tcp_ses_lock); + + if (tcon->ses) + server = tcon->ses->server; + + cifs_server_dbg(FYI, "tid=%u: tcon is closing, skipping async close retry of fid %llu %llu\n", + tcon->tid, persistent_fid, volatile_fid); + + return 0; + } tcon->tc_count++; spin_unlock(&cifs_tcp_ses_lock); -- 2.30.2