smb: client: fix mount when dns_resolver key is not available

commit 5e2fd17f434d2fed78efb123e2fc6711e4f598f1 upstream.

There was a wrong assumption that with CONFIG_CIFS_DFS_UPCALL=y there
would always be a dns_resolver key set up so we could unconditionally
upcall to resolve UNC hostname rather than using the value provided by
mount(2).

Only require it when performing automount of junctions within a DFS
share so users that don't have dns_resolver key still can mount their
regular shares with server hostname resolved by mount.cifs(8).

Fixes: 348a04a8d113 ("smb: client: get rid of dfs code dep in namespace.c")
Cc: stable@vger.kernel.org
Tested-by: Eduard Bachmakov <e.bachmakov@gmail.com>
Reported-by: Eduard Bachmakov <e.bachmakov@gmail.com>
Closes: https://lore.kernel.org/all/CADCRUiNvZuiUZ0VGZZO9HRyPyw6x92kiA7o7Q4tsX5FkZqUkKg@mail.gmail.com/
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/smb/client/dfs.c b/fs/smb/client/dfs.c
index 81b8415..a8a1d38 100644 (file)
--- a/fs/smb/client/dfs.c
+++ b/fs/smb/client/dfs.c
@@ -263,15 +263,23 @@ out:
        return rc;
 }
 
-/* Resolve UNC hostname in @ctx->source and set ip addr in @ctx->dstaddr */
+/*
+ * If @ctx->dfs_automount, then update @ctx->dstaddr earlier with the DFS root
+ * server from where we'll start following any referrals.  Otherwise rely on the
+ * value provided by mount(2) as the user might not have dns_resolver key set up
+ * and therefore failing to upcall to resolve UNC hostname under @ctx->source.
+ */
 static int update_fs_context_dstaddr(struct smb3_fs_context *ctx)
 {
        struct sockaddr *addr = (struct sockaddr *)&ctx->dstaddr;
-       int rc;
+       int rc = 0;
 
-       rc = dns_resolve_server_name_to_ip(ctx->source, addr, NULL);
-       if (!rc)
-               cifs_set_port(addr, ctx->port);
+       if (!ctx->nodfs && ctx->dfs_automount) {
+               rc = dns_resolve_server_name_to_ip(ctx->source, addr, NULL);
+               if (!rc)
+                       cifs_set_port(addr, ctx->port);
+               ctx->dfs_automount = false;
+       }
        return rc;
 }
 

diff --git a/fs/smb/client/fs_context.h b/fs/smb/client/fs_context.h
index 9d8d34a..cf46916 100644 (file)
--- a/fs/smb/client/fs_context.h
+++ b/fs/smb/client/fs_context.h
@@ -268,6 +268,7 @@ struct smb3_fs_context {
        bool witness:1; /* use witness protocol */
        char *leaf_fullpath;
        struct cifs_ses *dfs_root_ses;
+       bool dfs_automount:1; /* set for dfs automount only */
 };
 
 extern const struct fs_parameter_spec smb3_fs_parameters[];

diff --git a/fs/smb/client/namespace.c b/fs/smb/client/namespace.c
index c8f5ed8..a696857 100644 (file)
--- a/fs/smb/client/namespace.c
+++ b/fs/smb/client/namespace.c
@@ -117,6 +117,18 @@ cifs_build_devname(char *nodename, const char *prepath)
        return dev;
 }
 
+static bool is_dfs_mount(struct dentry *dentry)
+{
+       struct cifs_sb_info *cifs_sb = CIFS_SB(dentry->d_sb);
+       struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
+       bool ret;
+
+       spin_lock(&tcon->tc_lock);
+       ret = !!tcon->origin_fullpath;
+       spin_unlock(&tcon->tc_lock);
+       return ret;
+}
+
 /* Return full path out of a dentry set for automount */
 static char *automount_fullpath(struct dentry *dentry, void *page)
 {
@@ -212,8 +224,9 @@ static struct vfsmount *cifs_do_automount(struct path *path)
                ctx->source = NULL;
                goto out;
        }
-       cifs_dbg(FYI, "%s: ctx: source=%s UNC=%s prepath=%s\n",
-                __func__, ctx->source, ctx->UNC, ctx->prepath);
+       ctx->dfs_automount = is_dfs_mount(mntpt);
+       cifs_dbg(FYI, "%s: ctx: source=%s UNC=%s prepath=%s dfs_automount=%d\n",
+                __func__, ctx->source, ctx->UNC, ctx->prepath, ctx->dfs_automount);
 
        mnt = fc_mount(fc);
 out: