From cf3069a14a9cccdd89d2b482f9eee5e37ebe25a6 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 1 Jun 2016 11:55:05 +0200 Subject: [PATCH] proc: prevent stacking filesystems on top commit e54ad7f1ee263ffa5a2de9c609d58dfa27b21cd9 upstream. 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 Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- fs/proc/root.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/proc/root.c b/fs/proc/root.c index 03102d978180..c2f39abdbb7a 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -53,6 +53,13 @@ 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 (!sb->s_root) { sb->s_flags = flags; err = proc_fill_super(sb); -- 2.39.2