smb: client: fix UAF in smb2_reconnect_server()

commit 24a9799 upstream.

The UAF bug is due to smb2_reconnect_server() accessing a session that
is already being teared down by another thread that is executing
__cifs_put_smb_ses().  This can happen when (a) the client has
connection to the server but no session or (b) another thread ends up
setting @ses->ses_status again to something different than
SES_EXITING.

To fix this, we need to make sure to unconditionally set
@ses->ses_status to SES_EXITING and prevent any other threads from
setting a new status while we're still tearing it down.

The following can be reproduced by adding some delay to right after
the ipc is freed in __cifs_put_smb_ses() - which will give
smb2_reconnect_server() worker a chance to run and then accessing
@ses->ipc:

kinit ...
mount.cifs //srv/share /mnt/1 -o sec=krb5,nohandlecache,echo_interval=10
[disconnect srv]
ls /mnt/1 &>/dev/null
sleep 30
kdestroy
[reconnect srv]
sleep 10
umount /mnt/1
...
CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed
CIFS: VFS: \\srv Send error in SessSetup = -126
CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed
CIFS: VFS: \\srv Send error in SessSetup = -126
general protection fault, probably for non-canonical address
0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP NOPTI
CPU: 3 PID: 50 Comm: kworker/3:1 Not tainted 6.9.0-rc2 #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39
04/01/2014
Workqueue: cifsiod smb2_reconnect_server [cifs]
RIP: 0010:__list_del_entry_valid_or_report+0x33/0xf0
Code: 4f 08 48 85 d2 74 42 48 85 c9 74 59 48 b8 00 01 00 00 00 00 ad
de 48 39 c2 74 61 48 b8 22 01 00 00 00 00 74 69 <48> 8b 01 48 39 f8 75
7b 48 8b 72 08 48 39 c6 0f 85 88 00 00 00 b8
RSP: 0018:ffffc900001bfd70 EFLAGS: 00010a83
RAX: dead000000000122 RBX: ffff88810da53838 RCX: 6b6b6b6b6b6b6b6b
RDX: 6b6b6b6b6b6b6b6b RSI: ffffffffc02f6878 RDI: ffff88810da53800
RBP: ffff88810da53800 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff88810c064000
R13: 0000000000000001 R14: ffff88810c064000 R15: ffff8881039cc000
FS: 0000000000000000(0000) GS:ffff888157c00000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe3728b1000 CR3: 000000010caa4000 CR4: 0000000000750ef0
PKRU: 55555554
Call Trace:
 <TASK>
 ? die_addr+0x36/0x90
 ? exc_general_protection+0x1c1/0x3f0
 ? asm_exc_general_protection+0x26/0x30
 ? __list_del_entry_valid_or_report+0x33/0xf0
 __cifs_put_smb_ses+0x1ae/0x500 [cifs]
 smb2_reconnect_server+0x4ed/0x710 [cifs]
 process_one_work+0x205/0x6b0
 worker_thread+0x191/0x360
 ? __pfx_worker_thread+0x10/0x10
 kthread+0xe2/0x110
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x34/0x50
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>

Cc: stable@vger.kernel.org
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
[v5.10: added ses_lock to cifs_ses; used ses->status and old statusEnum values;
resolved contextual conflicts in cifs_put_smb_ses and moved changes from
cifs_mark_tcp_ses_conns_for_reconnect to cifs_reconnect]
Signed-off-by: Shaoying Xu <shaoyi@amazon.com>

Author: Paulo Alcantara

fs/cifs/cifsglob.h

@@ -979,6 +979,7 @@ struct cifs_ses {
 	struct list_head smb_ses_list;
 	struct list_head tcon_list;
 	struct cifs_tcon *tcon_ipc;
+	spinlock_t ses_lock;  /* protect anything here that is not protected */
 	struct mutex session_mutex;
 	struct TCP_Server_Info *server;	/* pointer to server info */
 	int ses_count;		/* reference counter */

fs/cifs/connect.c

@@ -455,6 +455,13 @@ cifs_reconnect(struct TCP_Server_Info *server)
 	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each(tmp, &server->smb_ses_list) {
 		ses = list_entry(tmp, struct cifs_ses, smb_ses_list);
+		spin_lock(&ses->ses_lock);
+		if (ses->status == CifsExiting) {
+			spin_unlock(&ses->ses_lock);
+			continue;
+		}
+		spin_unlock(&ses->ses_lock);
+
 		spin_lock(&ses->chan_lock);
 		if (cifs_chan_needs_reconnect(ses, server))
 			goto next_session;
@@ -2793,34 +2800,6 @@ cifs_setup_ipc(struct cifs_ses *ses, struct smb_vol *volume_info)
 	return rc;
 }
 
-/**
- * cifs_free_ipc - helper to release the session IPC tcon
- *
- * Needs to be called everytime a session is destroyed
- */
-static int
-cifs_free_ipc(struct cifs_ses *ses)
-{
-	int rc = 0, xid;
-	struct cifs_tcon *tcon = ses->tcon_ipc;
-
-	if (tcon == NULL)
-		return 0;
-
-	if (ses->server->ops->tree_disconnect) {
-		xid = get_xid();
-		rc = ses->server->ops->tree_disconnect(xid, tcon);
-		free_xid(xid);
-	}
-
-	if (rc)
-		cifs_dbg(FYI, "failed to disconnect IPC tcon (rc=%d)\n", rc);
-
-	tconInfoFree(tcon);
-	ses->tcon_ipc = NULL;
-	return rc;
-}
-
 static struct cifs_ses *
 cifs_find_smb_ses(struct TCP_Server_Info *server, struct smb_vol *vol)
 {
@@ -2845,28 +2824,43 @@ void cifs_put_smb_ses(struct cifs_ses *ses)
 	unsigned int rc, xid;
 	unsigned int chan_count;
 	struct TCP_Server_Info *server = ses->server;
+	struct cifs_tcon *tcon;
+	bool do_logoff;
 
 	cifs_dbg(FYI, "%s: ses_count=%d\n", __func__, ses->ses_count);
 
 	spin_lock(&cifs_tcp_ses_lock);
-	if (ses->status == CifsExiting) {
+	spin_lock(&ses->ses_lock);
+	cifs_dbg(FYI, "%s: id=0x%llx ses_count=%d ses_status=%u ipc=%s\n",
+		 __func__, ses->Suid, ses->ses_count, ses->status,
+		 ses->tcon_ipc ? ses->tcon_ipc->treeName : "none");
+	if (ses->status == CifsExiting || --ses->ses_count > 0) {
+		spin_unlock(&ses->ses_lock);
 		spin_unlock(&cifs_tcp_ses_lock);
 		return;
 	}
-	if (--ses->ses_count > 0) {
-		spin_unlock(&cifs_tcp_ses_lock);
-		return;
-	}
-	spin_unlock(&cifs_tcp_ses_lock);
 
-	spin_lock(&GlobalMid_Lock);
-	if (ses->status == CifsGood)
-		ses->status = CifsExiting;
-	spin_unlock(&GlobalMid_Lock);
+	spin_lock(&ses->chan_lock);
+	cifs_chan_clear_need_reconnect(ses, server);
+	spin_unlock(&ses->chan_lock);
 
-	cifs_free_ipc(ses);
+	do_logoff = ses->status == CifsGood && server->ops->logoff;
+	ses->status = CifsExiting;
+	tcon = ses->tcon_ipc;
+	ses->tcon_ipc = NULL;
+	spin_unlock(&ses->ses_lock);
+	spin_unlock(&cifs_tcp_ses_lock);
 
-	if (ses->status == CifsExiting && server->ops->logoff) {
+	/*
+	 * On session close, the IPC is closed and the server must release all
+	 * tcons of the session.  No need to send a tree disconnect here.
+	 *
+	 * Besides, it will make the server to not close durable and resilient
+	 * files on session close, as specified in MS-SMB2 3.3.5.6 Receiving an
+	 * SMB2 LOGOFF Request.
+	 */
+	tconInfoFree(tcon);
+	if (do_logoff) {
 		xid = get_xid();
 		rc = server->ops->logoff(xid, ses);
 		if (rc)