smb: client: fix double free of TCP_Server_Info::hostname

JIRA: https://issues.redhat.com/browse/RHEL-76046

commit fa2f990
Author: Paulo Alcantara <pc@manguebit.com>
Date:   Tue Jan 14 12:48:48 2025 -0300

    smb: client: fix double free of TCP_Server_Info::hostname
    
    When shutting down the server in cifs_put_tcp_session(), cifsd thread
    might be reconnecting to multiple DFS targets before it realizes it
    should exit the loop, so @server->hostname can't be freed as long as
    cifsd thread isn't done.  Otherwise the following can happen:
    
      RIP: 0010:__slab_free+0x223/0x3c0
      Code: 5e 41 5f c3 cc cc cc cc 4c 89 de 4c 89 cf 44 89 44 24 08 4c 89
      1c 24 e8 fb cf 8e 00 44 8b 44 24 08 4c 8b 1c 24 e9 5f fe ff ff <0f>
      0b 41 f7 45 08 00 0d 21 00 0f 85 2d ff ff ff e9 1f ff ff ff 80
      RSP: 0018:ffffb26180dbfd08 EFLAGS: 00010246
      RAX: ffff8ea34728e510 RBX: ffff8ea34728e500 RCX: 0000000000800068
      RDX: 0000000000800068 RSI: 0000000000000000 RDI: ffff8ea340042400
      RBP: ffffe112041ca380 R08: 0000000000000001 R09: 0000000000000000
      R10: 6170732e31303000 R11: 70726f632e786563 R12: ffff8ea34728e500
      R13: ffff8ea340042400 R14: ffff8ea34728e500 R15: 0000000000800068
      FS: 0000000000000000(0000) GS:ffff8ea66fd80000(0000)
      000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00007ffc25376080 CR3: 000000012a2ba001 CR4:
      PKRU: 55555554
      Call Trace:
       <TASK>
       ? show_trace_log_lvl+0x1c4/0x2df
       ? show_trace_log_lvl+0x1c4/0x2df
       ? __reconnect_target_unlocked+0x3e/0x160 [cifs]
       ? __die_body.cold+0x8/0xd
       ? die+0x2b/0x50
       ? do_trap+0xce/0x120
       ? __slab_free+0x223/0x3c0
       ? do_error_trap+0x65/0x80
       ? __slab_free+0x223/0x3c0
       ? exc_invalid_op+0x4e/0x70
       ? __slab_free+0x223/0x3c0
       ? asm_exc_invalid_op+0x16/0x20
       ? __slab_free+0x223/0x3c0
       ? extract_hostname+0x5c/0xa0 [cifs]
       ? extract_hostname+0x5c/0xa0 [cifs]
       ? __kmalloc+0x4b/0x140
       __reconnect_target_unlocked+0x3e/0x160 [cifs]
       reconnect_dfs_server+0x145/0x430 [cifs]
       cifs_handle_standard+0x1ad/0x1d0 [cifs]
       cifs_demultiplex_thread+0x592/0x730 [cifs]
       ? __pfx_cifs_demultiplex_thread+0x10/0x10 [cifs]
       kthread+0xdd/0x100
       ? __pfx_kthread+0x10/0x10
       ret_from_fork+0x29/0x50
       </TASK>
    
    Fixes: 7be3248 ("cifs: To match file servers, make sure the server hostname matches")
    Reported-by: Jay Shin <jaeshin@redhat.com>
    Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
    Signed-off-by: Steve French <stfrench@microsoft.com>

Signed-off-by: Paulo Alcantara <paalcant@redhat.com>

Author: pcacjr

fs/smb/client/connect.c

@@ -1046,6 +1046,7 @@ clean_demultiplex_info(struct TCP_Server_Info *server)
 	/* Release netns reference for this server. */
 	put_net(cifs_net_ns(server));
 	kfree(server->leaf_fullpath);
+	kfree(server->hostname);
 	kfree(server);
 
 	length = atomic_dec_return(&tcpSesAllocCount);
@@ -1672,8 +1673,6 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
 	kfree_sensitive(server->session_key.response);
 	server->session_key.response = NULL;
 	server->session_key.len = 0;
-	kfree(server->hostname);
-	server->hostname = NULL;
 
 	task = xchg(&server->tsk, NULL);
 	if (task)