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Wed, 21 Oct 2026 22:36:35 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id BuZaOnI+2WpvSgAAD6G6ig (envelope-from ); Wed, 21 Oct 2026 22:36:35 +0000 Message-ID: Date: Thu, 22 Oct 2026 00:36:26 +0200 X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v2 04/15] net: skbuff: fail segmentation when a segment can't be checksummed To: Josef Bacik , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Andrew Lunn Cc: Juergen Gross , Stefano Stabellini , Willem de Bruijn , Mina Almasry , David Laight , netdev@vger.kernel.org, xen-devel@lists.xenproject.org References: <20261021-b4-skbuff-bug-on-followups-v2-0-2aa780a03524@toxicpanda.com> <20261021-b4-skbuff-bug-on-followups-v2-4-2aa780a03524@toxicpanda.com> Content-Language: en-US From: Fernando Fernandez Mancera In-Reply-To: <20261021-b4-skbuff-bug-on-followups-v2-4-2aa780a03524@toxicpanda.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-11.79 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[suse.com,kernel.org,gmail.com,google.com,vger.kernel.org,lists.xenproject.org]; RCVD_COUNT_TWO(0.00)[2]; TAGGED_RCPT(0.00)[netdev]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[toxicpanda.com:email] X-Spam-Score: -11.79 X-Spam-Level: X-Spam-Flag: NO On 10/21/26 3:46 PM, Josef Bacik wrote: > When the device can't checksum the protocol, skb_segment() computes > each segment's checksum in software with skb_checksum(). With SG on, > the segments share the original frags, and a devmem TCP skb keeps its > whole payload in unreadable frags. The devmem MSG_ZEROCOPY path never > sets SKBFL_SHARED_FRAG, so the __skb_linearize() fallback is skipped > too. skb_checksum() then warns and returns 0, and tcp_gso_segment() > writes a TCP checksum that doesn't cover the payload that goes out. > > That's reachable with tx-checksumming off and SG on: sk_setup_caps() > still gives TCP SG and HW_CSUM, so the dmabuf send is accepted, and > harmonize_features() strips the checksum features but keeps SG. > > Use skb_checksum_full() and fail the segmentation with -EFAULT when it > can't checksum a segment, as skb_segment() already does when it can't > copy one. > > Found by the Sashiko AI review of an earlier fix for the same path with > SG off. > > Link: https://lore.kernel.org/all/20261009-b4-skb-segment-nosg-unreadable-v1-1-7e2334a55fe8@toxicpanda.com/ > Assisted-by: LLM > Signed-off-by: Josef Bacik > --- Reviewed-by: Fernando Fernandez Mancera Thanks! > net/core/skbuff.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 40d2dd20d47d..88ed2dd99dc0 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -5239,9 +5239,13 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, > > if (!nskb->remcsum_offload) > nskb->ip_summed = CHECKSUM_NONE; > - SKB_GSO_CB(nskb)->csum = > - skb_checksum(nskb, doffset, > - nskb->len - doffset, 0); > + SKB_GSO_CB(nskb)->csum = 0; > + if (skb_checksum_full(nskb, doffset, > + nskb->len - doffset, > + &SKB_GSO_CB(nskb)->csum)) { > + err = -EFAULT; > + goto err; > + } > SKB_GSO_CB(nskb)->csum_start = > skb_headroom(nskb) + doffset; > } >