From: Miklos Szeredi <mszeredi@redhat.com>
Date: Mon, 14 Dec 2020 14:26:14 +0000 (+0100)
Subject: ovl: check privs before decoding file handle
X-Git-Tag: accepted/tizen/unified/20230118.172025~8235^2~7
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c846af050f944d584f28bc0de310383003c8096d;p=platform%2Fkernel%2Flinux-rpi.git

ovl: check privs before decoding file handle

CAP_DAC_READ_SEARCH is required by open_by_handle_at(2) so check it in
ovl_decode_real_fh() as well to prevent privilege escalation for
unprivileged overlay mounts.

[Amir] If the mounter is not capable in init ns, ovl_check_origin() and
ovl_verify_index() will not function as expected and this will break index
and nfs export features.  So check capability in ovl_can_decode_fh(), to
auto disable those features.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 509dac7..3fe05fb 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -156,6 +156,9 @@ struct dentry *ovl_decode_real_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
 	struct dentry *real;
 	int bytes;
 
+	if (!capable(CAP_DAC_READ_SEARCH))
+		return NULL;
+
 	/*
 	 * Make sure that the stored uuid matches the uuid of the lower
 	 * layer where file handle will be decoded.
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 44b4b62..ced63c7 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -50,6 +50,9 @@ const struct cred *ovl_override_creds(struct super_block *sb)
  */
 int ovl_can_decode_fh(struct super_block *sb)
 {
+	if (!capable(CAP_DAC_READ_SEARCH))
+		return 0;
+
 	if (!sb->s_export_op || !sb->s_export_op->fh_to_dentry)
 		return 0;