From 570d7a98e7d6d5d8706d94ffd2d40adeaa318332 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Sat, 29 Jun 2019 13:27:44 -0700 Subject: [PATCH] vfs: move_mount: reject moving kernel internal mounts sys_move_mount() crashes by dereferencing the pointer MNT_NS_INTERNAL, a.k.a. ERR_PTR(-EINVAL), if the old mount is specified by fd for a kernel object with an internal mount, such as a pipe or memfd. Fix it by checking for this case and returning -EINVAL. [AV: what we want is is_mounted(); use that instead of making the condition even more convoluted] Reproducer: #include #define __NR_move_mount 429 #define MOVE_MOUNT_F_EMPTY_PATH 0x00000004 int main() { int fds[2]; pipe(fds); syscall(__NR_move_mount, fds[0], "", -1, "/", MOVE_MOUNT_F_EMPTY_PATH); } Reported-by: syzbot+6004acbaa1893ad013f0@syzkaller.appspotmail.com Fixes: 2db154b3ea8e ("vfs: syscall: Add move_mount(2) to move mounts around") Signed-off-by: Eric Biggers Signed-off-by: Al Viro --- fs/namespace.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 7660c2749c96..6fbc9126367a 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2596,11 +2596,12 @@ static int do_move_mount(struct path *old_path, struct path *new_path) if (!check_mnt(p)) goto out; - /* The thing moved should be either ours or completely unattached. */ - if (attached && !check_mnt(old)) + /* The thing moved must be mounted... */ + if (!is_mounted(&old->mnt)) goto out; - if (!attached && !(ns && is_anon_ns(ns))) + /* ... and either ours or the root of anon namespace */ + if (!(attached ? check_mnt(old) : is_anon_ns(ns))) goto out; if (old->mnt.mnt_flags & MNT_LOCKED)