[PATCH 5.10/5.15 1/1] smb: client: fix use-after-free bug in cifs_debug_data_proc_show()

[d.privalov <d.privalov@omp.ru>]

From: Paulo Alcantara <pc@manguebit.com>

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+0x36/0x90м
  [  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>
[d.privalov: Adapt checking status ses->ses_status to use global lock GlobalMid_Lock]
Signed-off-by: Dmitriy Privalov <d.privalov@omp.ru>
---
 fs/cifs/cifs_debug.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/cifs/cifs_debug.c b/fs/cifs/cifs_debug.c
index 53588d7517b4..c094f44fbbde 100644
--- a/fs/cifs/cifs_debug.c
+++ b/fs/cifs/cifs_debug.c
@@ -356,6 +356,11 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 		list_for_each(tmp2, &server->smb_ses_list) {
 			ses = list_entry(tmp2, struct cifs_ses,
 					 smb_ses_list);
+			spin_lock(&GlobalMid_Lock);
+			if (ses->status == CifsExiting) {
+				spin_unlock(&GlobalMid_Lock);
+				continue;
+			}
 			if ((ses->serverDomain == NULL) ||
 				(ses->serverOS == NULL) ||
 				(ses->serverNOS == NULL)) {
@@ -375,6 +380,7 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 				ses->capabilities, ses->status);
 			}
+			spin_unlock(&GlobalMid_Lock);
 
 			seq_printf(m,"Security type: %s\n",
 				get_security_type_str(server->ops->select_sectype(server, ses->sectype)));
 
-- 
2.34.1