Subject: Re: [PATCH net] net: fix __dst_negative_advice() race

From: Lee Jones <[email-masked]>
Date: Wed, 12 Jun 2024 16:52:35 +0100

On Tue, 28 May 2024, Eric Dumazet wrote:

> __dst_negative_advice() does not enforce proper RCU rules when
> sk->dst_cache must be cleared, leading to possible UAF.
> 
> RCU rules are that we must first clear sk->sk_dst_cache,
> then call dst_release(old_dst).
> 
> Note that sk_dst_reset(sk) is implementing this protocol correctly,
> while __dst_negative_advice() uses the wrong order.
> 
> Given that ip6_negative_advice() has special logic
> against RTF_CACHE, this means each of the three ->negative_advice()
> existing methods must perform the sk_dst_reset() themselves.
> 
> Note the check against NULL dst is centralized in
> __dst_negative_advice(), there is no need to duplicate
> it in various callbacks.
> 
> Many thanks to Clement Lecigne for tracking this issue.
> 
> This old bug became visible after the blamed commit, using UDP sockets.
> 
> Fixes: a87cb3e48ee8 ("net: Facility to report route quality of connected sockets")
> Reported-by: Clement Lecigne <[email-masked]>
> Diagnosed-by: Clement Lecigne <[email-masked]>
> Signed-off-by: Eric Dumazet <[email-masked]>
> Cc: Tom Herbert <[email-masked]>
> ---
>  include/net/dst_ops.h  |  2 +-
>  include/net/sock.h     | 13 +++----------
>  net/ipv4/route.c       | 22 ++++++++--------------
>  net/ipv6/route.c       | 29 +++++++++++++++--------------
>  net/xfrm/xfrm_policy.c | 11 +++--------
>  5 files changed, 30 insertions(+), 47 deletions(-)

Could we have this patch in all Stable branches please?

Upstream commit:

  Fixes: 92f1655aa2b2 ("net: fix __dst_negative_advice() race")

-- 
Lee Jones [李琼斯]