linux-kernel - Re: [PATCH net-next v1 1/4] net: netmem: fix skb_ensure

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Message-ID: <20250614113713.46b69771@kernel.org>
Date: Sat, 14 Jun 2025 11:37:13 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Mina Almasry <almasrymina@...gle.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon
 Horman <horms@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>, Shuah Khan
 <shuah@...nel.org>
Subject: Re: [PATCH net-next v1 1/4] net: netmem: fix skb_ensure_writable
 with unreadable skbs

On Fri, 13 Jun 2025 04:28:01 +0000 Mina Almasry wrote:
> skb_ensure_writable actually makes sure that the header of the skb is
> writable, and doesn't touch the payload. It doesn't need an
> skb_frags_readable check.

"doesn't touch the payload" is a bit misleading.
What I'd say instead is that the pskb_may_pull() call about ensures that
write_len is within the head, and will already fail if write_len would
dip into unreadable frags.

> Removing this check restores DSCP functionality with unreadable skbs as
> it's called from dscp_tg.
> 
> Fixes: 65249feb6b3d ("net: add support for skbs with unreadable frags")
> 
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>

Either no Fixes tag or send it to net. I think net is fine, this is
clearly incorrect. By definition devmem should not prevent header
modifications, so net?

nit: no empty lines between tags
-- 
pw-bot: cr