Re: [PATCH] Remove unused function parameter in __smc_diag_dump

[Jeongjun Park <aha310510@gmail.com>]

Manas <devnull+manas18244.iiitd.ac.in@kernel.org> wrote:
> The last parameter in __smc_diag_dump (struct nlattr *bc) is unused.
> There is only one instance of this function being called and its passed
> with a NULL value in place of bc.
> 
> Signed-off-by: Manas <manas18244@iiitd.ac.in>
> ---
> The last parameter in __smc_diag_dump (struct nlattr *bc) is unused.
> There is only one instance of this function being called and its passed
> with a NULL value in place of bc.
> 
> Though, the compiler (gcc) optimizes it. Looking at the object dump of
> vmlinux (via `objdump -D vmlinux`), a new function clone
> (__smc_diag_dump.constprop.0) is added which removes this parameter from
> calling convention altogether.
> 
> ffffffff8a701770 <__smc_diag_dump.constprop.0>:
> ffffffff8a701770:       41 57                   push   %r15
> ffffffff8a701772:       41 56                   push   %r14
> ffffffff8a701774:       41 55                   push   %r13
> ffffffff8a701776:       41 54                   push   %r12
> 
> There are 5 parameters in original function, but in the cloned function
> only 4.
> 
> I believe this patch also fixes this oops bug[1], which arises in the
> same function __smc_diag_dump. But I couldn't verify it further. Can
> someone please test this?
> 
> [1] https://syzkaller.appspot.com/bug?extid=271fed3ed6f24600c364

Unfortunately, I tested it myself and this bug is still triggering. Basically,
this bug is not triggered in normal situations, but triggered when a race
condition occurs, so I think the root cause is somewhere else.

Regards,

Jeongjun Park

> ---
>  net/smc/smc_diag.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/net/smc/smc_diag.c b/net/smc/smc_diag.c
> index 6fdb2d96777ad704c394709ec845f9ddef5e599a..8f7bd40f475945171a0afa5a2cce12d9aa2b1eb4 100644
> --- a/net/smc/smc_diag.c
> +++ b/net/smc/smc_diag.c
> @@ -71,8 +71,7 @@ static int smc_diag_msg_attrs_fill(struct sock *sk, struct sk_buff *skb,
>  
>  static int __smc_diag_dump(struct sock *sk, struct sk_buff *skb,
>  			   struct netlink_callback *cb,
> -			   const struct smc_diag_req *req,
> -			   struct nlattr *bc)
> +			   const struct smc_diag_req *req)
>  {
>  	struct smc_sock *smc = smc_sk(sk);
>  	struct smc_diag_fallback fallback;
> @@ -199,7 +198,6 @@ static int smc_diag_dump_proto(struct proto *prot, struct sk_buff *skb,
>  	struct smc_diag_dump_ctx *cb_ctx = smc_dump_context(cb);
>  	struct net *net = sock_net(skb->sk);
>  	int snum = cb_ctx->pos[p_type];
> -	struct nlattr *bc = NULL;
>  	struct hlist_head *head;
>  	int rc = 0, num = 0;
>  	struct sock *sk;
> @@ -214,7 +212,7 @@ static int smc_diag_dump_proto(struct proto *prot, struct sk_buff *skb,
>  			continue;
>  		if (num < snum)
>  			goto next;
> -		rc = __smc_diag_dump(sk, skb, cb, nlmsg_data(cb->nlh), bc);
> +		rc = __smc_diag_dump(sk, skb, cb, nlmsg_data(cb->nlh));
>  		if (rc < 0)
>  			goto out;
>  next:
> 
> ---
> base-commit: 59b723cd2adbac2a34fc8e12c74ae26ae45bf230
> change-id: 20241109-fix-oops-__smc_diag_dump-06ab3e9d39f4
> 
> Best regards,
> -- 
> Manas <manas18244@iiitd.ac.in>