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/Kconfig b/fs/overlayfs/Kconfig
index cbfc196..5ac4154 100644
--- a/fs/overlayfs/Kconfig
+++ b/fs/overlayfs/Kconfig
@@ -24,6 +24,16 @@
an overlay which has redirects on a kernel that doesn't support this
feature will have unexpected results.
+config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
+ bool "Overlayfs: follow redirects even if redirects are turned off"
+ default y
+ depends on OVERLAY_FS
+ help
+ Disable this to get a possibly more secure configuration, but that
+ might not be backward compatible with previous kernels.
+
+ For more information, see Documentation/filesystems/overlayfs.txt
+
config OVERLAY_FS_INDEX
bool "Overlayfs: turn on inodes index feature by default"
depends on OVERLAY_FS