[PATCH] btrfs-progs: enforce chroot for btrfs receive

["Lauri Võsandi" <lauri.vosandi@gmail.com>]

This patch forces btrfs receive to issue chroot before
parsing the btrfs stream to confine the process and
minimize damage that could be done via malicious
btrfs stream.

Signed-off-by: Lauri Võsandi <lauri.vosandi@gmail.com>
---
 cmds-receive.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/cmds-receive.c b/cmds-receive.c
index 44ef27e..8be92ea 100644
--- a/cmds-receive.c
+++ b/cmds-receive.c
@@ -867,15 +867,17 @@ static int do_receive(struct btrfs_receive *r, const char *tomnt, int r_fd,
 		goto out;
 	}
 
-	/*
-	 * find_mount_root returns a root_path that is a subpath of
-	 * dest_dir_full_path. Now get the other part of root_path,
-	 * which is the destination dir relative to root_path.
-	 */
-	r->dest_dir_path = dest_dir_full_path + strlen(r->root_path);
-	while (r->dest_dir_path[0] == '/')
-		r->dest_dir_path++;
+	if (chroot(dest_dir_full_path)) {
+		ret = -errno;
+		fprintf(stderr,
+			"ERROR: failed to chroot to %s, %s\n",
+			dest_dir_full_path,
+			strerror(-ret));
+		goto out;
+	}
 
+	r->root_path = r->dest_dir_path = strdup("/");
+	
 	ret = subvol_uuid_search_init(r->mnt_fd, &r->sus);
 	if (ret < 0)
 		goto out;
-- 
1.9.1