smb: client: Fix NULL pointer dereference in cifs_debug_dirs_proc_show()

Reading /proc/fs/cifs/open_dirs may hit a NULL dereference when
tcon->cfids is NULL.

Add NULL check before accessing cfids to prevent the crash.

Reproduction:
- Mount CIFS share
- cat /proc/fs/cifs/open_dirs

Fixes: 844e5c0eb176 ("smb3 client: add way to show directory leases for improved debugging")
Signed-off-by: Wang Zhaolong <wangzhaolong@huaweicloud.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/cifs_debug.c b/fs/smb/client/cifs_debug.c
index beb4f18f05ef1c0159ec854f95632adf0a1092bc..edb2e7f7fc23adf38ccfeae0311ca52dd5789545 100644 (file)
--- a/fs/smb/client/cifs_debug.c
+++ b/fs/smb/client/cifs_debug.c
@@ -304,6 +304,8 @@ static int cifs_debug_dirs_proc_show(struct seq_file *m, void *v)
                        list_for_each(tmp1, &ses->tcon_list) {
                                tcon = list_entry(tmp1, struct cifs_tcon, tcon_list);
                                cfids = tcon->cfids;
+                               if (!cfids)
+                                       continue;
                                spin_lock(&cfids->cfid_list_lock); /* check lock ordering */
                                seq_printf(m, "Num entries: %d\n", cfids->num_entries);
                                list_for_each_entry(cfid, &cfids->entries, entry) {
@@ -319,8 +321,6 @@ static int cifs_debug_dirs_proc_show(struct seq_file *m, void *v)
                                        seq_printf(m, "\n");
                                }
                                spin_unlock(&cfids->cfid_list_lock);
-
-
                        }
                }
        }