From: David Miller <davem@davemloft.net>
To: weichen.chen@linux.alibaba.com
Cc: eric.dumazet@gmail.com, kuba@kernel.org,
splendidsky.cwc@alibaba-inc.com, yanxu.zw@alibaba-inc.com,
dsahern@kernel.org, liuhangbin@gmail.com,
roopa@cumulusnetworks.com, jdike@akamai.com,
nikolay@cumulusnetworks.com, lirongqing@baidu.com,
mrv@mojatatu.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] net: neighbor: fix a crash caused by mod zero
Date: Mon, 28 Dec 2020 14:51:28 -0800 (PST) [thread overview]
Message-ID: <20201228.145128.1498314185351532341.davem@davemloft.net> (raw)
In-Reply-To: <20201225054448.73256-1-weichen.chen@linux.alibaba.com>
From: weichenchen <weichen.chen@linux.alibaba.com>
Date: Fri, 25 Dec 2020 13:44:45 +0800
> pneigh_enqueue() tries to obtain a random delay by mod
> NEIGH_VAR(p, PROXY_DELAY). However, NEIGH_VAR(p, PROXY_DELAY)
> migth be zero at that point because someone could write zero
> to /proc/sys/net/ipv4/neigh/[device]/proxy_delay after the
> callers check it.
>
> This patch uses prandom_u32_max() to get a random delay instead
> which avoids potential division by zero.
>
> Signed-off-by: weichenchen <weichen.chen@linux.alibaba.com>
> ---
> V4:
> - Use prandom_u32_max() to get a random delay in
> pneigh_enqueue().
> V3:
> - Callers need to pass the delay time to pneigh_enqueue()
> now and they should guarantee it is not zero.
> - Use READ_ONCE() to read NEIGH_VAR(p, PROXY_DELAY) in both
> of the existing callers of pneigh_enqueue() and then pass
> it to pneigh_enqueue().
> V2:
> - Use READ_ONCE() to prevent the complier from re-reading
> NEIGH_VAR(p, PROXY_DELAY).
> - Give a hint to the complier that delay <= 0 is unlikely
> to happen.
>
> V4 is quite concise and works well.
> Thanks for Eric's and Jakub's advice.
Applied and queued up for -stable, thanks.
prev parent reply other threads:[~2020-12-28 23:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-18 4:20 [PATCH] net: neighbor: fix a crash caused by mod zero weichenchen
2020-12-19 18:21 ` Jakub Kicinski
2020-12-21 13:07 ` [PATCH v2] " weichenchen
2020-12-21 19:32 ` Jakub Kicinski
2020-12-22 12:38 ` [PATCH v3] " weichenchen
2020-12-22 16:34 ` Eric Dumazet
2020-12-25 5:44 ` [PATCH v4] " weichenchen
2020-12-28 22:51 ` David Miller [this message]
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