Re: [PATCH net] crypto: chtls: Fix possible null pointer dereferences

[Jacob Keller]

On 4/9/2024 2:05 AM, Aleksandr Mishin wrote:
> In chtls_pass_accept_rpl() and chtls_select_mss() __sk_dst_get() may
> return NULL which is later dereferenced. Fix this bug by adding NULL check.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: cc35c88ae4db ("crypto : chtls - CPL handler definition")
> Signed-off-by: Aleksandr Mishin <amishin@xxxxxxxxxx>

This seems to do a lot more than simply adding a NULL check, though I
guess thats because it needs to pass the return out somehow properly? I
would have liked more explanation of the requires changes.



> ---
>  .../chelsio/inline_crypto/chtls/chtls_cm.c    | 24 +++++++++++++------
>  1 file changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
> index 6f6525983130..6d88cbc9fbb0 100644
> --- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
> +++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
> @@ -939,15 +939,15 @@ static void chtls_accept_rpl_arp_failure(void *handle,
>  	sock_put(sk);
>  }
>  
> -static unsigned int chtls_select_mss(const struct chtls_sock *csk,
> +static bool chtls_select_mss(const struct chtls_sock *csk,
>  				     unsigned int pmtu,
> -				     struct cpl_pass_accept_req *req)
> +				     struct cpl_pass_accept_req *req,
> +					 unsigned int *mtu_idx)
>  {
>  	struct chtls_dev *cdev;
>  	struct dst_entry *dst;
>  	unsigned int tcpoptsz;
>  	unsigned int iphdrsz;
> -	unsigned int mtu_idx;
>  	struct tcp_sock *tp;
>  	unsigned int mss;
>  	struct sock *sk;
> @@ -955,6 +955,9 @@ static unsigned int chtls_select_mss(const struct chtls_sock *csk,
>  	mss = ntohs(req->tcpopt.mss);
>  	sk = csk->sk;
>  	dst = __sk_dst_get(sk);
> +	if (!dst)
> +		return false;
> +
>  	cdev = csk->cdev;
>  	tp = tcp_sk(sk);
>  	tcpoptsz = 0;
> @@ -979,11 +982,11 @@ static unsigned int chtls_select_mss(const struct chtls_sock *csk,
>  	tp->advmss = cxgb4_best_aligned_mtu(cdev->lldi->mtus,
>  					    iphdrsz + tcpoptsz,
>  					    tp->advmss - tcpoptsz,
> -					    8, &mtu_idx);
> +					    8, mtu_idx);
>  	tp->advmss -= iphdrsz;
>  
>  	inet_csk(sk)->icsk_pmtu_cookie = pmtu;
> -	return mtu_idx;
> +	return true;
>  }
>  
>  static unsigned int select_rcv_wscale(int space, int wscale_ok, int win_clamp)
> @@ -1016,8 +1019,13 @@ static void chtls_pass_accept_rpl(struct sk_buff *skb,
>  	struct sock *sk;
>  	u32 opt2, hlen;
>  	u64 opt0;
> +	struct dst_entry *dst;
>  
>  	sk = skb->sk;
> +	dst = __sk_dst_get(sk);
> +	if (!dst)
> +		return;
> +
>  	tp = tcp_sk(sk);
>  	csk = sk->sk_user_data;
>  	csk->tid = tid;
> @@ -1029,8 +1037,10 @@ static void chtls_pass_accept_rpl(struct sk_buff *skb,
>  
>  	OPCODE_TID(rpl5) = cpu_to_be32(MK_OPCODE_TID(CPL_PASS_ACCEPT_RPL,
>  						     csk->tid));
> -	csk->mtu_idx = chtls_select_mss(csk, dst_mtu(__sk_dst_get(sk)),
> -					req);
> +	if (!chtls_select_mss(csk, dst_mtu(dst),
> +					req, &csk->mtu_idx))
> +		return;
> +
>  	opt0 = TCAM_BYPASS_F |
>  	       WND_SCALE_V(RCV_WSCALE(tp)) |
>  	       MSS_IDX_V(csk->mtu_idx) |