From 007ea44892e6fa963a0876a979e34890325c64eb Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Fri, 26 Oct 2018 23:34:39 +0200
Subject: [PATCH] ovl: relax permission checking on underlying layers
Make permission checking more consistent:
- special files don't need any access check on underling fs
- exec permission check doesn't need to be performed on underlying fs
Reported-by: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
fs/overlayfs/inode.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 3b7ed5d2279c6..6bcc9dedc342c 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -286,13 +286,22 @@ int ovl_permission(struct inode *inode, int mask)
if (err)
return err;
- old_cred = ovl_override_creds(inode->i_sb);
- if (!upperinode &&
- !special_file(realinode->i_mode) && mask & MAY_WRITE) {
+ /* No need to do any access on underlying for special files */
+ if (special_file(realinode->i_mode))
+ return 0;
+
+ /* No need to access underlying for execute */
+ mask &= ~MAY_EXEC;
+ if ((mask & (MAY_READ | MAY_WRITE)) == 0)
+ return 0;
+
+ /* Lower files get copied up, so turn write access into read */
+ if (!upperinode && mask & MAY_WRITE) {
mask &= ~(MAY_WRITE | MAY_APPEND);
- /* Make sure mounter can read file for copy up later */
mask |= MAY_READ;
}
+
+ old_cred = ovl_override_creds(inode->i_sb);
err = inode_permission(realinode, mask);
revert_creds(old_cred);
--
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