blob: 7cf2e92ee0a8aeb8e2c6ece1a7da3ca43e1ac1df [file] [log] [blame]
From 7a3efdd8d6f46febc0b6f5adf07f93781bf4e15e Mon Sep 17 00:00:00 2001
From: Piotr Krysiuk <piotras@gmail.com>
Date: Mon, 27 Apr 2020 11:34:12 +0100
Subject: [PATCH] fs/namespace.c: fix mountpoint reference counter race
A race condition between threads updating mountpoint reference counter
affects longterm releases 4.4.220, 4.9.220, 4.14.177 and 4.19.118.
The mountpoint reference counter corruption may occur when:
* one thread increments m_count member of struct mountpoint
[under namespace_sem, but not holding mount_lock]
pivot_root()
* another thread simultaneously decrements the same m_count
[under mount_lock, but not holding namespace_sem]
put_mountpoint()
unhash_mnt()
umount_mnt()
mntput_no_expire()
To fix this race condition, grab mount_lock before updating m_count in
pivot_root().
Reference: CVE-2020-12114
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Piotr Krysiuk <piotras@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[PG: use v4.19.119-stable version vs. backporting v5.3 VFS changes.]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/fs/namespace.c b/fs/namespace.c
index 6fbc9126367a..1508a402ce14 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3646,8 +3646,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
/* make certain new is below the root */
if (!is_path_reachable(new_mnt, new.dentry, &root))
goto out4;
- root_mp->m_count++; /* pin it so it won't go away */
lock_mount_hash();
+ root_mp->m_count++; /* pin it so it won't go away */
detach_mnt(new_mnt, &parent_path);
detach_mnt(root_mnt, &root_parent);
if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
--
2.7.4