cifs: fix potential race when tree connecting ipc

Protect access of TCP_Server_Info::hostname when building the ipc tree
name as it might get freed in cifsd thread and thus causing an
use-after-free bug in __tree_connect_dfs_target().  Also, while at it,
update status of IPC tcon on success and then avoid any extra tree
connects.

Cc: stable@vger.kernel.org # v6.2+
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/dfs.c b/fs/cifs/dfs.c
index 3a11716b6e13eb4b724177265a343981b26143a4..37f7da4f5c8b0f2f10e31a5ad3246ee9489e5cd2 100644 (file)
--- a/fs/cifs/dfs.c
+++ b/fs/cifs/dfs.c
@@ -374,6 +374,54 @@ static int target_share_matches_server(struct TCP_Server_Info *server, char *sha
        return rc;
 }
 
+static void __tree_connect_ipc(const unsigned int xid, char *tree,
+                              struct cifs_sb_info *cifs_sb,
+                              struct cifs_ses *ses)
+{
+       struct TCP_Server_Info *server = ses->server;
+       struct cifs_tcon *tcon = ses->tcon_ipc;
+       int rc;
+
+       spin_lock(&ses->ses_lock);
+       spin_lock(&ses->chan_lock);
+       if (cifs_chan_needs_reconnect(ses, server) ||
+           ses->ses_status != SES_GOOD) {
+               spin_unlock(&ses->chan_lock);
+               spin_unlock(&ses->ses_lock);
+               cifs_server_dbg(FYI, "%s: skipping ipc reconnect due to disconnected ses\n",
+                               __func__);
+               return;
+       }
+       spin_unlock(&ses->chan_lock);
+       spin_unlock(&ses->ses_lock);
+
+       cifs_server_lock(server);
+       scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
+       cifs_server_unlock(server);
+
+       rc = server->ops->tree_connect(xid, ses, tree, tcon,
+                                      cifs_sb->local_nls);
+       cifs_server_dbg(FYI, "%s: tree_reconnect %s: %d\n", __func__, tree, rc);
+       spin_lock(&tcon->tc_lock);
+       if (rc) {
+               tcon->status = TID_NEED_TCON;
+       } else {
+               tcon->status = TID_GOOD;
+               tcon->need_reconnect = false;
+       }
+       spin_unlock(&tcon->tc_lock);
+}
+
+static void tree_connect_ipc(const unsigned int xid, char *tree,
+                            struct cifs_sb_info *cifs_sb,
+                            struct cifs_tcon *tcon)
+{
+       struct cifs_ses *ses = tcon->ses;
+
+       __tree_connect_ipc(xid, tree, cifs_sb, ses);
+       __tree_connect_ipc(xid, tree, cifs_sb, CIFS_DFS_ROOT_SES(ses));
+}
+
 static int __tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *tcon,
                                     struct cifs_sb_info *cifs_sb, char *tree, bool islink,
                                     struct dfs_cache_tgt_list *tl)
@@ -382,7 +430,6 @@ static int __tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *t
        struct TCP_Server_Info *server = tcon->ses->server;
        const struct smb_version_operations *ops = server->ops;
        struct cifs_ses *root_ses = CIFS_DFS_ROOT_SES(tcon->ses);
-       struct cifs_tcon *ipc = root_ses->tcon_ipc;
        char *share = NULL, *prefix = NULL;
        struct dfs_cache_tgt_iterator *tit;
        bool target_match;
@@ -418,18 +465,14 @@ static int __tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *t
                }
 
                dfs_cache_noreq_update_tgthint(server->current_fullpath + 1, tit);
-
-               if (ipc->need_reconnect) {
-                       scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
-                       rc = ops->tree_connect(xid, ipc->ses, tree, ipc, cifs_sb->local_nls);
-                       cifs_dbg(FYI, "%s: reconnect ipc: %d\n", __func__, rc);
-               }
+               tree_connect_ipc(xid, tree, cifs_sb, tcon);
 
                scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
                if (!islink) {
                        rc = ops->tree_connect(xid, tcon->ses, tree, tcon, cifs_sb->local_nls);
                        break;
                }
+
                /*
                 * If no dfs referrals were returned from link target, then just do a TREE_CONNECT
                 * to it.  Otherwise, cache the dfs referral and then mark current tcp ses for