smb: client: fix use-after-free bug in cifs_debug_data_proc_show()

commit d328c09ee9f15ee5a26431f5aad7c9239fa85e62 upstream.

Skip SMB sessions that are being teared down
(e.g. @ses->ses_status == SES_EXITING) in cifs_debug_data_proc_show()
to avoid use-after-free in @ses.

This fixes the following GPF when reading from /proc/fs/cifs/DebugData
while mounting and umounting

  [ 816.251274] general protection fault, probably for non-canonical
  address 0x6b6b6b6b6b6b6d81: 0000 [#1] PREEMPT SMP NOPTI
  ...
  [  816.260138] Call Trace:
  [  816.260329]  <TASK>
  [  816.260499]  ? die_addr+0x36/0x90
  [  816.260762]  ? exc_general_protection+0x1b3/0x410
  [  816.261126]  ? asm_exc_general_protection+0x26/0x30
  [  816.261502]  ? cifs_debug_tcon+0xbd/0x240 [cifs]
  [  816.261878]  ? cifs_debug_tcon+0xab/0x240 [cifs]
  [  816.262249]  cifs_debug_data_proc_show+0x516/0xdb0 [cifs]
  [  816.262689]  ? seq_read_iter+0x379/0x470
  [  816.262995]  seq_read_iter+0x118/0x470
  [  816.263291]  proc_reg_read_iter+0x53/0x90
  [  816.263596]  ? srso_alias_return_thunk+0x5/0x7f
  [  816.263945]  vfs_read+0x201/0x350
  [  816.264211]  ksys_read+0x75/0x100
  [  816.264472]  do_syscall_64+0x3f/0x90
  [  816.264750]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
  [  816.265135] RIP: 0033:0x7fd5e669d381

Cc: stable@vger.kernel.org
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
[ This patch removed lock/unlock operation due to ses_lock is
not present in v5.10 and not ported yet. ses->status is protected
by a global lock, cifs_tcp_ses_lock, in v5.10. ]
Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
Signed-off-by: He Zhe <zhe.he@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/cifs/cifs_debug.c b/fs/cifs/cifs_debug.c
index 8b88b07054814629b65e79acabda2589ae849aad..e98755968bba51c6fffacc0a5c705752e2750c07 100644 (file)
--- a/fs/cifs/cifs_debug.c
+++ b/fs/cifs/cifs_debug.c
@@ -358,6 +358,8 @@ skip_rdma:
                list_for_each(tmp2, &server->smb_ses_list) {
                        ses = list_entry(tmp2, struct cifs_ses,
                                         smb_ses_list);
+                       if (ses->status == CifsExiting)
+                               continue;
                        if ((ses->serverDomain == NULL) ||
                                (ses->serverOS == NULL) ||
                                (ses->serverNOS == NULL)) {