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ovl: relax permission checking on underlying layers

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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>
This commit is contained in:
Miklos Szeredi 2018-10-26 23:34:39 +02:00
parent 6cd078702f
commit 007ea44892
1 changed files with 13 additions and 4 deletions
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17
fs/overlayfs/inode.c
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@ -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);