From 4667058b772857069378aa8f417203156e315e82 Mon Sep 17 00:00:00 2001
From: Gusev Vitaliy <gusev.vitaliy@nexenta.com>
Date: Wed, 23 Mar 2011 00:40:25 +0300
Subject: nfs4: Fix NULL dereference at d_alloc_and_lookup()

d_alloc_and_lookup() calls i_op->lookup method due to
rootfh changes his fsid.

During mount i_op of NFS root inode is set to
nfs_mountpoint_inode_operations, if rpc_ops->getroot()
and rpc_ops->getattr() return different fsid.

After that  nfs_follow_remote_path() raised oops:

   BUG: unable to handle kernel NULL pointer dereference at (null)
   IP: [<          (null)>]           (null)

stack trace:

     d_alloc_and_lookup+0x4c/0x74
     do_lookup+0x1e3/0x280
     link_path_walk+0x12e/0xab0
     nfs4_remote_get_sb+0x56/0x2c0 [nfs]
     path_walk+0x67/0xe0
     vfs_path_lookup+0x8e/0x100
     nfs_follow_remote_path+0x16f/0x3e0 [nfs]
     nfs4_try_mount+0x6f/0xd0 [nfs]
     nfs_get_sb+0x269/0x400 [nfs]
     vfs_kern_mount+0x8a/0x1f0
     do_kern_mount+0x52/0x130
     do_mount+0x20a/0x260
     sys_mount+0x90/0xe0
     system_call_fastpath+0x16/0x1b

So just refresh fsid, as RFC3530 doesn't specify behavior
in case of rootfh changes fsid.

Signed-off-by: Vitaliy Gusev <gusev.vitaliy@nexenta.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c
index b5ffe8f..7979652 100644
--- a/fs/nfs/getroot.c
+++ b/fs/nfs/getroot.c
@@ -199,6 +199,10 @@ struct dentry *nfs4_get_root(struct super_block *sb, struct nfs_fh *mntfh)
 		goto out;
 	}
 
+	if (fattr->valid & NFS_ATTR_FATTR_FSID &&
+	    !nfs_fsid_equal(&server->fsid, &fattr->fsid))
+		memcpy(&server->fsid, &fattr->fsid, sizeof(server->fsid));
+
 	inode = nfs_fhget(sb, mntfh, fattr);
 	if (IS_ERR(inode)) {
 		dprintk("nfs_get_root: get root inode failed\n");
-- 
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