FAILED: patch "[PATCH] smb: client: cancel reconnect work in" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x c65eae6f61d1778ff7a82e4aae4080e26f486af1
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026092200-operating-swinger-d7a7@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c65eae6f61d1778ff7a82e4aae4080e26f486af1 Mon Sep 17 00:00:00 2001
From: Paulo Alcantara <[email protected]>
Date: Fri, 11 Sep 2026 22:38:04 -0300
Subject: [PATCH] smb: client: cancel reconnect work in
clean_demultiplex_info()

clean_demultiplex_info() cancels server->echo delayed work but not server->reconnect, which can cause a use-after-free when the demultiplex thread exits while a reconnect work is still queued:

cifs_demultiplex_thread()

    cifs_readv_from_socket()
      cifs_reconnect()
        __cifs_reconnect()
          cifs_queue_server_reconn()
            mod_delayed_work(cifsiod_wq, &server->reconnect, 0)
    clean_demultiplex_info()
      cancel_delayed_work_sync(&server->echo)   // echo canceled
                                                 // reconnect NOT canceled
      kfree_sensitive(server)                    // server freed

...later, on cifsiod_wq:

smb2_reconnect_server()

    server->srv_count  // UAF read of freed server

Fix this by canceling server->reconnect delayed work in clean_demultiplex_info() before the server is freed, the same way cifs_put_tcp_session() already does.

index b6e98eb31673..bef710d9a3c3 100644
@@ -1067,6 +1067,7 @@ clean_demultiplex_info(struct TCP_Server_Info *server)
 	spin_unlock(&server->srv_lock);
 
 	cancel_delayed_work_sync(&server->echo);
+	cancel_delayed_work_sync(&server->reconnect);
 
 	spin_lock(&server->srv_lock);
 	server->tcpStatus = CifsExiting;

From: Paulo Alcantara <[email protected]>

[ Upstream commit 0e9bd27b2a635d54665fcc1d6398a5f6aeb6b0cb ]

We already upcall to resolve hostnames during reconnect by calling reconn_set_ipaddr_from_hostname(), so there is no point in having a worker to periodically call it.

Reviewed-by <[email protected]>

Backport to 5.15: keep the existing string-returning DNS resolver, address conversion, and cifs_tcp_ses_lock protection. Remove the DNS worker, its scheduling and cancellation, and its interval constants. Drop the sess.c hunk because this tree has no explicit DNS-work cancellation in cifs_ses_add_channel(); it uses cifs_put_tcp_session(). Do not import the newer interface-polling or reconnect helpers.

This leaves clean_demultiplex_info() ready for the reconnect-work cancellation in c65eae6f61d1778ff7a82e4aae4080e26f486af1.

[ sashal: Reduced backport -- upstream 0e9bd27b2a635 touches 3 file(s), this
backport carries 2. Not backported here:
fs/cifs/sess.c
This note is generated from the file lists only; see the resolution record for the reasoning. ]

Stable-dep-of: c65eae6f61d1 ("smb: client: cancel reconnect work in clean_demultiplex_info()")

---
 fs/cifs/cifsglob.h |  5 -----
 fs/cifs/connect.c  | 54 +++-------------------------------------------
 2 files changed, 3 insertions(+), 56 deletions(-)

index 9b08020634f19..019ce688c1943 100644
@@ -78,10 +78,6 @@
 #define SMB_ECHO_INTERVAL_MAX 600
 #define SMB_ECHO_INTERVAL_DEFAULT 60
 
-/* dns resolution intervals in seconds */
-#define SMB_DNS_RESOLVE_INTERVAL_MIN     120
-#define SMB_DNS_RESOLVE_INTERVAL_DEFAULT 600
-
 /* maximum number of PDUs in one compound */
 #define MAX_COMPOUND 5
 

@@ -651,7 +647,6 @@ struct TCP_Server_Info {
 	/* point to the SMBD connection if RDMA is used instead of socket */
 	struct smbd_connection *smbd_conn;
 	struct delayed_work	echo; /* echo ping workqueue job */
-	struct delayed_work	resolve; /* dns resolution workqueue job */
 	char	*smallbuf;	/* pointer to current "small" buffer */
 	char	*bigbuf;	/* pointer to current "big" buffer */
 	/* Total size of this PDU. Only valid from cifs_demultiplex_thread */

2.53.0

From: Paulo Alcantara <[email protected]>

[ Upstream commit c65eae6f61d1778ff7a82e4aae4080e26f486af1 ]

clean_demultiplex_info() cancels server->echo delayed work but not server->reconnect, which can cause a use-after-free when the demultiplex thread exits while a reconnect work is still queued:

cifs_demultiplex_thread()

    cifs_readv_from_socket()
      cifs_reconnect()
        __cifs_reconnect()
          cifs_queue_server_reconn()
            mod_delayed_work(cifsiod_wq, &server->reconnect, 0)
    clean_demultiplex_info()
      cancel_delayed_work_sync(&server->echo)   // echo canceled
                                                 // reconnect NOT canceled
      kfree_sensitive(server)                    // server freed

...later, on cifsiod_wq:

smb2_reconnect_server()

    server->srv_count  // UAF read of freed server

Fix this by canceling server->reconnect delayed work in clean_demultiplex_info() before the server is freed, the same way cifs_put_tcp_session() already does.

---
 fs/cifs/connect.c | 1 +
 1 file changed, 1 insertion(+)

index 424cc901fb27a..19d4ea7359da4 100644
@@ -725,6 +725,7 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
 	spin_unlock(&cifs_tcp_ses_lock);
 
 	cancel_delayed_work_sync(&server->echo);
+	cancel_delayed_work_sync(&server->reconnect);
 
 	spin_lock(&GlobalMid_Lock);
 	server->tcpStatus = CifsExiting;

2.53.0