>From a57429c935ed0d5484a8c51795694bb61a3c1008 Mon Sep 17 00:00:00 2001 From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> Date: Sat, 26 Dec 2015 21:54:58 -0500 Subject: [PATCH 2/2] NFSv4: Don't perform cached access checks before we've OPENed the file [ commit 762674f86d0328d5dc923c966e209e1ee59663f2 upstream ] Donald Buczek reports that a nfs4 client incorrectly denies execute access based on outdated file mode (missing 'x' bit). After the mode on the server is 'fixed' (chmod +x) further execution attempts continue to fail, because the nfs ACCESS call updates the access parameter but not the mode parameter or the mode in the inode. The root cause is ultimately that the VFS is calling may_open() before the NFS client has a chance to OPEN the file and hence revalidate the access and attribute caches. Al Viro suggests: >>> Make nfs_permission() relax the checks when it sees MAY_OPEN, if you know >>> that things will be caught by server anyway? >> >> That can work as long as we're guaranteed that everything that calls >> inode_permission() with MAY_OPEN on a regular file will also follow up >> with a vfs_open() or dentry_open() on success. Is this always the >> case? > > 1) in do_tmpfile(), followed by do_dentry_open() (not reachable by NFS since > it doesn't have ->tmpfile() instance anyway) > > 2) in atomic_open(), after the call of ->atomic_open() has succeeded. > > 3) in do_last(), followed on success by vfs_open() > > That's all. All calls of inode_permission() that get MAY_OPEN come from > may_open(), and there's no other callers of that puppy. Reported-by: Donald Buczek <buczek@xxxxxxxxxxxxx> Link: https://bugzilla.kernel.org/show_bug.cgi?id=109771 Link: http://lkml.kernel.org/r/1451046656-26319-1-git-send-email-buczek@xxxxxxxxxxxxx Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> Signed-off-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx> --- fs/nfs/dir.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index 2d7c451..5b21b1c 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -2452,6 +2452,9 @@ int nfs_permission(struct inode *inode, int mask) case S_IFLNK: goto out; case S_IFREG: + if ((mask & MAY_OPEN) && + nfs_server_capable(inode, NFS_CAP_ATOMIC_OPEN)) + return 0; break; case S_IFDIR: /* -- 2.4.1