cifs: fix possible uninitialized access and race on iface_list

iface[0] was accessed regardless of the count value and without
locking.

* check count before accessing any ifaces
* make copy of iface list (it's a simple POD array) and use it without
  locking.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>

diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index d951373..f0795c8 100644 (file)
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -77,6 +77,8 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
        int i = 0;
        int rc = 0;
        int tries = 0;
+       struct cifs_server_iface *ifaces = NULL;
+       size_t iface_count;
 
        if (left <= 0) {
                cifs_dbg(FYI,
@@ -91,6 +93,26 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
        }
 
        /*
+        * Make a copy of the iface list at the time and use that
+        * instead so as to not hold the iface spinlock for opening
+        * channels
+        */
+       spin_lock(&ses->iface_lock);
+       iface_count = ses->iface_count;
+       if (iface_count <= 0) {
+               spin_unlock(&ses->iface_lock);
+               cifs_dbg(FYI, "no iface list available to open channels\n");
+               return 0;
+       }
+       ifaces = kmemdup(ses->iface_list, iface_count*sizeof(*ifaces),
+                        GFP_ATOMIC);
+       if (!ifaces) {
+               spin_unlock(&ses->iface_lock);
+               return 0;
+       }
+       spin_unlock(&ses->iface_lock);
+
+       /*
         * Keep connecting to same, fastest, iface for all channels as
         * long as its RSS. Try next fastest one if not RSS or channel
         * creation fails.
@@ -105,9 +127,9 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
                        break;
                }
 
-               iface = &ses->iface_list[i];
+               iface = &ifaces[i];
                if (is_ses_using_iface(ses, iface) && !iface->rss_capable) {
-                       i = (i+1) % ses->iface_count;
+                       i = (i+1) % iface_count;
                        continue;
                }
 
@@ -115,7 +137,7 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
                if (rc) {
                        cifs_dbg(FYI, "failed to open extra channel on iface#%d rc=%d\n",
                                 i, rc);
-                       i = (i+1) % ses->iface_count;
+                       i = (i+1) % iface_count;
                        continue;
                }
 
@@ -124,6 +146,7 @@ int cifs_try_adding_channels(struct cifs_ses *ses)
                left--;
        }
 
+       kfree(ifaces);
        return ses->chan_count - old_chan_count;
 }