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ovl: simplify permission checking

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The fact that we always do permission checking on the overlay inode and
clear MAY_WRITE for checking access to the lower inode allows cruft to be
removed from ovl_permission().

1) "default_permissions" option effectively did generic_permission() on the
overlay inode with i_mode, i_uid and i_gid updated from underlying
filesystem.  This is what we do by default now.  It did the update using
vfs_getattr() but that's only needed if the underlying filesystem can
change (which is not allowed).  We may later introduce a "paranoia_mode"
that verifies that mode/uid/gid are not changed.

2) splitting out the IS_RDONLY() check from inode_permission() also becomes
unnecessary once we remove the MAY_WRITE from the lower inode check.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi
2016-07-29 12:05:23 +02:00
parent 754f8cb72b
commit 9c630ebefe
3 changed files with 1 additions and 53 deletions
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46
fs/overlayfs/inode.c
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@@ -124,29 +124,6 @@ int ovl_permission(struct inode *inode, int mask)
const struct cred *old_cred;
int err;
if (ovl_is_default_permissions(inode)) {
struct kstat stat;
struct path realpath = { .dentry = realdentry };
if (mask & MAY_NOT_BLOCK)
return -ECHILD;
realpath.mnt = ovl_entry_mnt_real(oe, inode, is_upper);
err = vfs_getattr(&realpath, &stat);
if (err)
return err;
if ((stat.mode ^ inode->i_mode) & S_IFMT)
return -ESTALE;
inode->i_mode = stat.mode;
inode->i_uid = stat.uid;
inode->i_gid = stat.gid;
return generic_permission(inode, mask);
}
/* Careful in RCU walk mode */
realinode = d_inode_rcu(realdentry);
if (!realinode) {
@@ -154,27 +131,6 @@ int ovl_permission(struct inode *inode, int mask)
return -ENOENT;
}
if (mask & MAY_WRITE) {
umode_t mode = realinode->i_mode;
/*
* Writes will always be redirected to upper layer, so
* ignore lower layer being read-only.
*
* If the overlay itself is read-only then proceed
* with the permission check, don't return EROFS.
* This will only happen if this is the lower layer of
* another overlayfs.
*
* If upper fs becomes read-only after the overlay was
* constructed return EROFS to prevent modification of
* upper layer.
*/
if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
(S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
return -EROFS;
}
/*
* Check overlay inode with the creds of task and underlying inode
* with creds of mounter
@@ -186,7 +142,7 @@ int ovl_permission(struct inode *inode, int mask)
old_cred = ovl_override_creds(inode->i_sb);
if (!is_upper)
mask &= ~(MAY_WRITE | MAY_APPEND);
err = __inode_permission(realinode, mask);
err = inode_permission(realinode, mask);
revert_creds(old_cred);
return err;