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SubjectRe: [PATCH] ipv6_sockglue: Fix a missing-check bug in ip6_ra_control()
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On 24. 05. 19, 5:19, Gen Zhang wrote:
> In function ip6_ra_control(), the pointer new_ra is allocated a memory
> space via kmalloc(). And it is used in the following codes. However,
> when there is a memory allocation error, kmalloc() fails. Thus null
> pointer dereference may happen. And it will cause the kernel to crash.
> Therefore, we should check the return value and handle the error.
>
> Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
>
> ---
> diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> index 40f21fe..0a3d035 100644
> --- a/net/ipv6/ipv6_sockglue.c
> +++ b/net/ipv6/ipv6_sockglue.c
> @@ -68,6 +68,8 @@ int ip6_ra_control(struct sock *sk, int sel)
> return -ENOPROTOOPT;
>
> new_ra = (sel >= 0) ? kmalloc(sizeof(*new_ra), GFP_KERNEL) : NULL;
> + if (sel >= 0 && !new_ra)
> + return -ENOMEM;
>
> write_lock_bh(&ip6_ra_lock);
> for (rap = &ip6_ra_chain; (ra = *rap) != NULL; rap = &ra->next) {
>

Was this really an omission? There is (!new_ra) handling below the for loop:
if (!new_ra) {
write_unlock_bh(&ip6_ra_lock);
return -ENOBUFS;
}

It used to handle both (sel >= 0) and (sel == 0) cases and it used to
return ENOBUFS in case of failure. For (sel >= 0) it also could at least
return EADDRINUSE when a collision was found -- even if memory was
exhausted.

In anyway, how could this lead to a pointer dereference? And why/how did
this get a CVE number?

thanks,
--
js
suse labs

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