NFS: Fix a possible Oops in fs/nfs/super.c

Sigh... commit 4584f520e1f773082ef44ff4f8969a5d992b16ec (NFS: Fix NFS
mountpoint crossing...) had a slight flaw: server can be NULL if sget()
returned an existing superblock.

Fix the fix by dereferencing s->s_fs_info.

Thanks to Coverity/Adrian Bunk and Frank Filz for spotting the bug.
(See http://bugzilla.kernel.org/show_bug.cgi?id=9647)

Also add in the same namespace Oops fix for NFSv4 in both the mountpoint
crossing case, and the referral case.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index ea929207f274..0b0c72a072ff 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1475,7 +1475,7 @@ static int nfs_xdev_get_sb(struct file_system_type *fs_type, int flags,
                 error = PTR_ERR(mntroot);
                 goto error_splat_super;
         }
-        if (mntroot->d_inode->i_op != server->nfs_client->rpc_ops->dir_inode_ops) {
+        if (mntroot->d_inode->i_op != NFS_SB(s)->nfs_client->rpc_ops->dir_inode_ops) {
                 dput(mntroot);
                 error = -ESTALE;
                 goto error_splat_super;
@@ -1826,6 +1826,11 @@ static int nfs4_xdev_get_sb(struct file_system_type *fs_type, int flags,
                 error = PTR_ERR(mntroot);
                 goto error_splat_super;
         }
+        if (mntroot->d_inode->i_op != NFS_SB(s)->nfs_client->rpc_ops->dir_inode_ops) {
+                dput(mntroot);
+                error = -ESTALE;
+                goto error_splat_super;
+        }
 
         s->s_flags |= MS_ACTIVE;
         mnt->mnt_sb = s;
@@ -1900,6 +1905,11 @@ static int nfs4_referral_get_sb(struct file_system_type *fs_type, int flags,
                 error = PTR_ERR(mntroot);
                 goto error_splat_super;
         }
+        if (mntroot->d_inode->i_op != NFS_SB(s)->nfs_client->rpc_ops->dir_inode_ops) {
+                dput(mntroot);
+                error = -ESTALE;
+                goto error_splat_super;
+        }
 
         s->s_flags |= MS_ACTIVE;
         mnt->mnt_sb = s;