From e54ad7f1ee263ffa5a2de9c609d58dfa27b21cd9 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 1 Jun 2016 11:55:05 +0200 Subject: proc: prevent stacking filesystems on top This prevents stacking filesystems (ecryptfs and overlayfs) from using procfs as lower filesystem. There is too much magic going on inside procfs, and there is no good reason to stack stuff on top of procfs. (For example, procfs does access checks in VFS open handlers, and ecryptfs by design calls open handlers from a kernel thread that doesn't drop privileges or so.) Signed-off-by: Jann Horn Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds --- fs/proc/root.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/proc/root.c b/fs/proc/root.c index 361ab4e..ec649c9 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -121,6 +121,13 @@ static struct dentry *proc_mount(struct file_system_type *fs_type, if (IS_ERR(sb)) return ERR_CAST(sb); + /* + * procfs isn't actually a stacking filesystem; however, there is + * too much magic going on inside it to permit stacking things on + * top of it + */ + sb->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH; + if (!proc_parse_options(options, ns)) { deactivate_locked_super(sb); return ERR_PTR(-EINVAL); -- cgit v1.1