Netdev Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Eric Dumazet <edumazet@google.com>
To: Tim Gardner <tim.gardner@canonical.com>
Cc: netdev <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	David Ahern <dsahern@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH linux-next] ipv4: Fix NULL deference in fnhe_remove_oldest()
Date: Thu, 2 Sep 2021 09:38:26 -0700	[thread overview]
Message-ID: <CANn89i+ey++b=dBXUZjXYyVessr49yZJBagVJxP-mpcreYyjCA@mail.gmail.com> (raw)
In-Reply-To: <20210902163205.17164-1-tim.gardner@canonical.com>

On Thu, Sep 2, 2021 at 9:32 AM Tim Gardner <tim.gardner@canonical.com> wrote:
>
> Coverity complains that linux-next commit 67d6d681e15b5 ("ipv4: make
> exception cache less predictible") neglected to check for NULL before
> dereferencing 'oldest'. It appears to be possible to fall through the for
> loop without ever setting 'oldest'.

Coverity is wrong.

 fnhe_remove_oldest() is only called when there are at least 6 items
in the list.

There is no way oldest could be NULL, or that oldest_p could contain garbage.

>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
> Cc: David Ahern <dsahern@kernel.org>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: netdev@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
> ---
>  net/ipv4/route.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index d6899ab5fb39..e85026591a09 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -603,9 +603,11 @@ static void fnhe_remove_oldest(struct fnhe_hash_bucket *hash)
>                         oldest_p = fnhe_p;
>                 }
>         }
> -       fnhe_flush_routes(oldest);
> -       *oldest_p = oldest->fnhe_next;
> -       kfree_rcu(oldest, rcu);
> +       if (oldest) {
> +               fnhe_flush_routes(oldest);
> +               *oldest_p = oldest->fnhe_next;
> +               kfree_rcu(oldest, rcu);
> +       }
>  }
>
>  static u32 fnhe_hashfun(__be32 daddr)
> --
> 2.33.0
>

  reply	other threads:[~2021-09-02 16:38 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-02 16:32 Tim Gardner
2021-09-02 16:38 ` Eric Dumazet [this message]
2021-09-02 16:41   ` David Ahern

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CANn89i+ey++b=dBXUZjXYyVessr49yZJBagVJxP-mpcreYyjCA@mail.gmail.com' \
    --to=edumazet@google.com \
    --cc=davem@davemloft.net \
    --cc=dsahern@kernel.org \
    --cc=kuba@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=tim.gardner@canonical.com \
    --cc=yoshfuji@linux-ipv6.org \
    --subject='Re: [PATCH linux-next] ipv4: Fix NULL deference in fnhe_remove_oldest()' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).