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Subject[PATCH 4.2.y-ckt 251/268] NFS: Ensure we revalidate attributes before using execute_ok()
Date
4.2.8-ckt3 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Trond Myklebust <trond.myklebust@primarydata.com>

commit 5c5fc09a1157a11dbe84e6421c3e0b37d05238cb upstream.

Donald Buczek reports that NFS clients can also report incorrect
results for access() due to lack of revalidation of attributes
before calling execute_ok().
Looking closely, it seems chdir() is afflicted with the same problem.

Fix is to ensure we call nfs_revalidate_inode_rcu() or
nfs_revalidate_inode() as appropriate before deciding to trust
execute_ok().

Reported-by: Donald Buczek <buczek@molgen.mpg.de>
Link: http://lkml.kernel.org/r/1451331530-3748-1-git-send-email-buczek@molgen.mpg.de
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/nfs/dir.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 40d0dc6..fccbda7 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -2443,6 +2443,20 @@ int nfs_may_open(struct inode *inode, struct rpc_cred *cred, int openflags)
}
EXPORT_SYMBOL_GPL(nfs_may_open);

+static int nfs_execute_ok(struct inode *inode, int mask)
+{
+ struct nfs_server *server = NFS_SERVER(inode);
+ int ret;
+
+ if (mask & MAY_NOT_BLOCK)
+ ret = nfs_revalidate_inode_rcu(server, inode);
+ else
+ ret = nfs_revalidate_inode(server, inode);
+ if (ret == 0 && !execute_ok(inode))
+ ret = -EACCES;
+ return ret;
+}
+
int nfs_permission(struct inode *inode, int mask)
{
struct rpc_cred *cred;
@@ -2495,8 +2509,8 @@ force_lookup:
res = PTR_ERR(cred);
}
out:
- if (!res && (mask & MAY_EXEC) && !execute_ok(inode))
- res = -EACCES;
+ if (!res && (mask & MAY_EXEC))
+ res = nfs_execute_ok(inode, mask);

dfprintk(VFS, "NFS: permission(%s/%lu), mask=0x%x, res=%d\n",
inode->i_sb->s_id, inode->i_ino, mask, res);
--
1.9.1
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