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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45eb6d4741bsm25849304f8f.22.2026.05.25.00.28.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 25 May 2026 00:28:28 -0700 (PDT) Message-ID: <27a64a78-f94a-4724-8bb6-3eba84204df8@gmail.com> Date: Mon, 25 May 2026 08:28:26 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] net: gro: don't copy frags between mixed zcopy skbs To: Sabrina Dubroca Cc: netdev@vger.kernel.org, Huzaifa Sidhpurwala , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Willem de Bruijn References: <4d583fc5401298453d0a2f1b4719a15be30c8e49.1779194090.git.sd@queasysnail.net> <743e314d-abfd-4a03-a74e-33a57c0bf6b8@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/19/26 15:59, Sabrina Dubroca wrote: > 2026-05-19, 15:39:19 +0100, Pavel Begunkov wrote: >> On 5/19/26 13:40, Sabrina Dubroca wrote: >>> skb_gro_receive() can currently copy frags between the source and GRO >>> skb, without checking the zerocopy status, and in particular the >>> SKBFL_MANAGED_FRAG_REFS flag. >>> >>> When SKBFL_MANAGED_FRAG_REFS is set, the skb doesn't hold a reference >>> on the pages in shinfo->frags. Appending those frags to another skb's >>> frags without fixing up the page refcount can lead to UAF. >>> >>> When either the last skb in the GRO chain (the one we would append >>> frags to) or the source skb is zerocopy, skip the frags copy, and just >>> append the new skb to the frag_list. >> >> Was it reproduced? Sounds like we're missing skb_orphan_frags_rx() >> as skbs looping into rx should be orphaned. >> >> +cc Willem > > Yes, as I wrote in the patch: > > Huzaifa has found this to be exploitable to overwrite the page cache I know, I know, but I had to ask as since recently there are too many reports where the exact wording wouldn't mean anything sensible. Thanks for clarifying! -- Pavel Begunkov