From: Piotr Krysiuk Date: Mon, 27 Apr 2020 11:34:12 +0100 Subject: fs/namespace.c: fix mountpoint reference counter race Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f511dc75d22e0c000fc70b54f670c2c17f5fba9a Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-12114 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 Signed-off-by: Piotr Krysiuk Signed-off-by: Greg Kroah-Hartman --- fs/namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/namespace.c b/fs/namespace.c index 1fce41ba3535..741f40cd955e 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3142,8 +3142,8 @@ 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) { -- 2.27.0.rc0