From: Piotr Krysiuk Date: Mon, 27 Apr 2020 10:34:12 +0000 (+0100) Subject: fs/namespace.c: fix mountpoint reference counter race X-Git-Tag: v3.16.84~100 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=172f22d527862eb5aa9dd767826f5d68562943db;p=thirdparty%2Fkernel%2Fstable.git 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 Signed-off-by: Piotr Krysiuk Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- diff --git a/fs/namespace.c b/fs/namespace.c index 5acf789efbab2..8c41f38617dbb 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2937,8 +2937,8 @@ 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) {