[PATCH] nfs: check a crash in nfs_lookup_revalidate

[Peng Huang]

lookup_one_len() may call nfs_loopup_revalidate() with nd == NULL
indirectly, that causes the kernel crash.

RIP: 0010:[<ffffffffa0ba3b41>]  [<ffffffffa0ba3b41>]
nfs_lookup_revalidate+0x21/0x4a0 [nfs]
RSP: 0018:ffff88018f00fae8  EFLAGS: 00010286

Call Trace:
 [<ffffffff81164a17>] do_revalidate+0x17/0x60
 [<ffffffff81164e9b>] __lookup_hash+0xcb/0x140
 [<ffffffff811653c4>] lookup_one_len+0x94/0xe0
 [<ffffffff81241ef1>] ecryptfs_lookup+0x91/0x1d0
 [<ffffffff81164d85>] d_alloc_and_lookup+0x45/0x90
 [<ffffffff8116f7b5>] ? d_lookup+0x35/0x60
 [<ffffffff811669b2>] do_lookup+0x192/0x2d0
 [<ffffffff811763be>] ? vfsmount_lock_local_unlock+0x1e/0x30
 [<ffffffff8126d09c>] ? security_inode_permission+0x1c/0x30
 [<ffffffff81167d67>] link_path_walk+0x597/0xae0
 [<ffffffff8117638e>] ? vfsmount_lock_local_lock+0x1e/0x30
 [<ffffffff81165905>] ? path_init_rcu+0xa5/0x210
 [<ffffffff8116858b>] do_path_lookup+0x5b/0x140
 [<ffffffff811692f7>] user_path_at+0x57/0xa0
 [<ffffffff8159fd08>] ? do_page_fault+0x1e8/0x4e0
 [<ffffffff8115eb86>] vfs_fstatat+0x46/0x80
 [<ffffffff8116b990>] ? filldir+0x0/0xe0
 [<ffffffff8115ec2e>] vfs_lstat+0x1e/0x20
 [<ffffffff8115ec54>] sys_newlstat+0x24/0x50
 [<ffffffff8159c995>] ? page_fault+0x25/0x30
 [<ffffffff8100bfc2>] system_call_fastpath+0x16/0x1b

Signed-off-by: Peng Huang <shawn.p.huang@xxxxxxxxx>
---
 fs/nfs/dir.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 2c3eb33..9452aa5 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1028,7 +1028,7 @@ static int nfs_lookup_revalidate(struct dentry *dentry, struct nameidata *nd)
 	struct nfs_fattr *fattr = NULL;
 	int error;
 
-	if (nd->flags & LOOKUP_RCU)
+	if (nd != NULL && nd->flags & LOOKUP_RCU)
 		return -ECHILD;
 
 	parent = dget_parent(dentry);
-- 
1.7.1

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