ovl: don't follow redirects if redirect_dir=off
Overlayfs is following redirects even when redirects are disabled. If this
is unintentional (probably the majority of cases) then this can be a
problem. E.g. upper layer comes from untrusted USB drive, and attacker
crafts a redirect to enable read access to otherwise unreadable
directories.
If "redirect_dir=off", then turn off following as well as creation of
redirects. If "redirect_dir=follow", then turn on following, but turn off
creation of redirects (which is what "redirect_dir=off" does now).
This is a backward incompatible change, so make it dependent on a config
option.
Reported-by: David Howells <dhowells@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 752bab6..9d0bc03 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -14,6 +14,8 @@ struct ovl_config {
char *workdir;
bool default_permissions;
bool redirect_dir;
+ bool redirect_follow;
+ const char *redirect_mode;
bool index;
};