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Mon, 03 Aug 2026 10:31:28 -0700 (PDT) Date: Mon, 3 Aug 2026 10:31:25 -0700 From: Bobby Eshleman To: Mina Almasry Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, kerneljasonxing@gmail.com, kuniyu@google.com, bjorn@kernel.org, jiayuan.chen@linux.dev, kaiyuanz@google.com, willemb@google.com, asml.silence@gmail.com, sdf@fomichev.me, fw@strlen.de, Neal Cardwell , Ralf Lici , Will Deacon Subject: Re: [PATCH net v2 1/3] net: core: propagate unreadable flag in skb_zerocopy Message-ID: References: <20260803171441.408014-1-almasrymina@google.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260803171441.408014-1-almasrymina@google.com> On Mon, Aug 03, 2026 at 05:14:39PM +0000, Mina Almasry wrote: > When skb_zerocopy() copies devmem payload fragments, it fails to update > the target skb's unreadable flag. This causes the target to appear as > readable memory. > > Propagate the unreadable flag if any devmem fragments were copied from > the source. > > Additionally, to prevent memory corruption, explicitly return -EFAULT > if standard payload from the head is mixed into the same skb alongside > unreadable devmem fragments during a head-to-frag extraction. > > Fixes: 65249feb6b3d ("net: add support for skbs with unreadable frags") > Cc: Pavel Begunkov > Cc: Stanislav Fomichev > Cc: Bobby Eshleman > Cc: Florian Westphal > Signed-off-by: Mina Almasry > Reviewed-by: Pavel Begunkov > > --- > v2: > - Return -EFAULT when mixing head-to-frag unreadable/readable frags to prevent memory corruption (Pavel). > v1: https://lore.kernel.org/r/20260801125308.1342897-1-almasrymina@google.com > --- > net/core/skbuff.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index ba3dbac80fb49..8bacc6c4e16e1 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -3905,6 +3905,9 @@ skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen) > } > } > > + if (!skb_frags_readable(from) && j > 0 && len) > + return -EFAULT; > + > skb_len_add(to, len + plen); > > if (unlikely(skb_orphan_frags(from, GFP_ATOMIC))) { > @@ -3928,6 +3931,9 @@ skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen) > } > skb_shinfo(to)->nr_frags = j; > > + if (i > 0 && from->unreadable) > + to->unreadable = 1; > + > return 0; > } > EXPORT_SYMBOL_GPL(skb_zerocopy); > > base-commit: af39eb111ce6b5eba9c08513b62c4868eb7e7fd5 > -- > 2.55.0.571.g244d577d93-goog > Reviewed-by: Bobby Eshleman