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Tue, 28 Jul 2026 08:30:43 -0700 (PDT) Date: Tue, 28 Jul 2026 08:30:42 -0700 From: Joe Damato To: Jiangshan Yi Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, stefanha@redhat.com, mst@redhat.com, will@kernel.org, ralf@mandelbit.com, viro@zeniv.linux.org.uk, kuniyu@google.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, 13667453960@163.com, stable@vger.kernel.org Subject: Re: [PATCH] net: datagram: fix integer overflow in zerocopy_sg_from_iter Message-ID: Mail-Followup-To: Joe Damato , Jiangshan Yi , davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, stefanha@redhat.com, mst@redhat.com, will@kernel.org, ralf@mandelbit.com, viro@zeniv.linux.org.uk, kuniyu@google.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, 13667453960@163.com, stable@vger.kernel.org References: <20260728064235.337877-1-yijiangshan@kylinos.cn> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260728064235.337877-1-yijiangshan@kylinos.cn> On Tue, Jul 28, 2026 at 02:42:35PM +0800, Jiangshan Yi wrote: > zerocopy_sg_from_iter() computes the copy length as: > > copy = min_t(int, skb_headlen(skb), iov_iter_count(from)); > > iov_iter_count() returns size_t. When it exceeds INT_MAX (e.g. via > io_uring provided buffers), the int cast wraps negative, wins the min() idk I looked at the code and it looks to be capped at INT_MAX, so i'm not sure that the io_uring example could ever happen ? I think the commit message misstates what is actually possible > comparison, and the negative copy propagates into > skb_copy_datagram_from_iter(), which can trigger WARN_ON or corrupt > data. > > Use min_t(size_t, ...) so the comparison is done in the correct type. > The result is always <= skb_headlen(skb), which fits in int. > Fixes: 3a654f975bf9 ("new helpers: skb_copy_datagram_from_iter() and zerocopy_sg_from_iter()") > Cc: stable@vger.kernel.org > Signed-off-by: Jiangshan Yi > --- > net/core/datagram.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/core/datagram.c b/net/core/datagram.c > index c285c6465923..fd8e17d25a3d 100644 > --- a/net/core/datagram.c > +++ b/net/core/datagram.c > @@ -783,7 +783,7 @@ EXPORT_SYMBOL(__zerocopy_sg_from_iter); > */ > int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from) > { > - int copy = min_t(int, skb_headlen(skb), iov_iter_count(from)); > + int copy = min_t(size_t, skb_headlen(skb), iov_iter_count(from)); I don't get this. Wouldn't copy need to also be a size_t to be consistent with the general "idea" of this patch ? If you leave copy as an int aren't you just shifting the alleged overflow to the assignment ? Even if you changed copy to a size_t then..... > > /* copy up to skb headlen */ > if (skb_copy_datagram_from_iter(skb, 0, from, copy)) this would still be a problem because len here is an int ? I feel like if you really wanna fix this you would have to use min3 or something instead of min_t ? But, I'd probably just leave it and not propose a patch to change this at all.