NFSv4: Ensure that we check lock exclusive/shared type against open modes

Since we may be simulating flock() locks using NFS byte range locks,
we can't rely on the VFS having checked the file open mode for us.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org

1 files changed, 14 insertions, 0 deletions

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 3c787d02131b..ba837d977a1a 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -4726,6 +4726,20 @@ nfs4_proc_lock(struct file *filp, int cmd, struct file_lock *request)
 
         if (state == NULL)
                 return -ENOLCK;
+        /*
+         * Don't rely on the VFS having checked the file open mode,
+         * since it won't do this for flock() locks.
+         */
+        switch (request->fl_type & (F_RDLCK|F_WRLCK|F_UNLCK)) {
+        case F_RDLCK:
+                if (!(filp->f_mode & FMODE_READ))
+                        return -EBADF;
+                break;
+        case F_WRLCK:
+                if (!(filp->f_mode & FMODE_WRITE))
+                        return -EBADF;
+        }
+
         do {
                 status = nfs4_proc_setlk(state, cmd, request);
                 if ((status != -EAGAIN) || IS_SETLK(cmd))