Re: [bpf-next v2 1/2] bpf: skmsg, fix psock create on existing kcm/tls port

[Eric Dumazet <eric.dumazet@gmail.com>]

On 10/17/2018 10:20 PM, John Fastabend wrote:
> Before using the psock returned by sk_psock_get() when adding it to a
> sockmap we need to ensure it is actually a sockmap based psock.
> Previously we were only checking this after incrementing the reference
> counter which was an error. This resulted in a slab-out-of-bounds
> error when the psock was not actually a sockmap type.
> 
> This moves the check up so the reference counter is only used
> if it is a sockmap psock.
> 
> Eric reported the following KASAN BUG,
> 
> BUG: KASAN: slab-out-of-bounds in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
> BUG: KASAN: slab-out-of-bounds in refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120
> Read of size 4 at addr ffff88019548be58 by task syz-executor4/22387
> 
> CPU: 1 PID: 22387 Comm: syz-executor4 Not tainted 4.19.0-rc7+ #264
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
>  print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
>  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
>  check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
>  kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272
>  atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
>  refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120
>  sk_psock_get include/linux/skmsg.h:379 [inline]
>  sock_map_link.isra.6+0x41f/0xe30 net/core/sock_map.c:178
>  sock_hash_update_common+0x19b/0x11e0 net/core/sock_map.c:669
>  sock_hash_update_elem+0x306/0x470 net/core/sock_map.c:738
>  map_update_elem+0x819/0xdf0 kernel/bpf/syscall.c:818
> 
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
> ---
>  include/linux/skmsg.h | 25 ++++++++++++++++++++-----
>  net/core/sock_map.c   | 11 ++++++-----
>  2 files changed, 26 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> index 677b673..f44ca6b 100644
> --- a/include/linux/skmsg.h
> +++ b/include/linux/skmsg.h
> @@ -275,11 +275,6 @@ static inline struct sk_psock *sk_psock(const struct sock *sk)
>  	return rcu_dereference_sk_user_data(sk);
>  }
>  
> -static inline bool sk_has_psock(struct sock *sk)
> -{
> -	return sk_psock(sk) != NULL && sk->sk_prot->recvmsg == tcp_bpf_recvmsg;
> -}
> -
>  static inline void sk_psock_queue_msg(struct sk_psock *psock,
>  				      struct sk_msg *msg)
>  {
> @@ -379,6 +374,26 @@ static inline bool sk_psock_test_state(const struct sk_psock *psock,
>  	return test_bit(bit, &psock->state);
>  }
>  
> +static inline struct sk_psock *sk_psock_get_checked(struct sock *sk)
> +{
> +	struct sk_psock *psock;
> +
> +	rcu_read_lock();
> +	psock = sk_psock(sk);
> +	if (psock) {
> +		if (sk->sk_prot->recvmsg != tcp_bpf_recvmsg) {
> +			psock = ERR_PTR(-EBUSY);
> +			goto out;
> +		}
> +
> +		if (!refcount_inc_not_zero(&psock->refcnt))
> +			psock = NULL;

Caller is using IS_ERR(), so you probably want to :

			psock = ERR_PTR(-E<something>);



> +	}
> +out:
> +	rcu_read_unlock();
> +	return psock;
> +}
> +
>  static inline struct sk_psock *sk_psock_get(struct sock *sk)
>  {
>  	struct sk_psock *psock;
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 3c0e44c..be6092a 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -175,12 +175,13 @@ static int sock_map_link(struct bpf_map *map, struct sk_psock_progs *progs,
>  		}
>  	}
>  
> -	psock = sk_psock_get(sk);
> +	psock = sk_psock_get_checked(sk);
> +	if (IS_ERR(psock)) {
> +		ret = PTR_ERR(psock);
> +		goto out_progs;
> +	}
> +
>  	if (psock) {
> -		if (!sk_has_psock(sk)) {
> -			ret = -EBUSY;
> -			goto out_progs;
> -		}
>  		if ((msg_parser && READ_ONCE(psock->progs.msg_parser)) ||
>  		    (skb_progs  && READ_ONCE(psock->progs.skb_parser))) {
>  			sk_psock_put(sk, psock);
>