On 29.12.2015 01:40, Trond Myklebust wrote:
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@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1451331530-3748-1-git-send-email-buczek@xxxxxxxxxxxxx
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
---
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 44e519c21e18..5bd2f5bfaf57 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -2432,6 +2432,20 @@ 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;
@@ -2484,8 +2498,8 @@ 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);
This patch doesn't resolve the problem. The reason is, that there is a
nfs_do_access() before this nfs_execute_ok() in the execution path of
nfs_permission. While nfs4_proc_acccess doesn't update the mode, it
does update read_cache_jiffies. So the later nfs_revalidate_inode will
be a noop, the cache was just made to look fresh.
If nfs_revalidate_inode would be called before the nfs_do_access it
might work. I fact it would make some sense to move it before the switch
based on inode->i_mode, because the mode might change on the server, too.
Regards
Donald
PS: Sorry for my faulty patch! What a shame :(
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