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Mon, 24 Aug 2026 03:31:23 -0700 (PDT) Received: from localhost ([188.216.77.92]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c24d6f203acsm166444066b.24.2026.08.24.03.31.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Aug 2026 03:31:23 -0700 (PDT) Date: Mon, 24 Aug 2026 12:31:22 +0200 From: Lorenzo Bianconi To: Jiayuan Chen Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, syzbot+237bbeed8dfe0699b7f5@syzkaller.appspotmail.com, Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Simon Horman , Martin KaFai Lau , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Shuah Khan , Kuniyuki Iwashima , Hangbin Liu , Krishna Kumar , Martin Karsten , Toke =?iso-8859-1?Q?H=F8iland-J=F8rgensen?= , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH bpf v2 1/2] bpf, veth: xdp: fix page_pool page leak on skb-backed XDP Message-ID: References: <20260824030257.263179-1-jiayuan.chen@linux.dev> <20260824030705.266049-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="upSIBUhSliXFFaM1" Content-Disposition: inline In-Reply-To: <20260824030705.266049-1-jiayuan.chen@linux.dev> X-Proofpoint-GUID: 4zJDCQqzoJLLU0nvCx2mSoie_vTdlG6h X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI0MDA4NyBTYWx0ZWRfXw+LjDK9+YQT+ YT3grB3ArjEy1FmDHL/DwxclUsdvQu7dM9ikwNf5cfs3CyclfheuLGJXOWYtggn4lueyzStxbNN NDH16TPu6WAIrbvjTp56KLYsIz9x7C6P8HIv5oPUTyEmaqinDMxHe8GmqdbrA5++n1wyoC3w/JV eJNMQBzzg5T6l4hnkRAeahF9vaStqZoI4O66qmDv0pP4gSFvbVc1EESIff86DemV6Sf6T15TqBo LjQf1eYCSLGjzMaHZdCBv4ZgZBWhIE+7RhHA/pHd9Z8uP3mEdtMeLEHXgfCYpLQOVY97y0vFu+e rM6OgotPJhjhE3Yq8uMMIi3LD60/tzJ0kFQfoxI6zQofdayttX8RfC1ZT4QtyIbLE+13w9cGMRN 3vfqfxvyq+rMfXA8RBV1eDQ3YHrrh1XSDOrFeZb1So41cQ2WaD6vNUeo8tmIblsgWFi9PNw50Sw PkkG8Axfm3y4D3NvkIg== X-Authority-Analysis: v=2.4 cv=Fqo1OWrq c=1 sm=1 tr=0 ts=6a8c1d7d cx=c_pps a=EVbN6Ke/fEF3bsl7X48z0g==:117 a=WpTaRW6qxYHRGzLzQsVYzg==:17 a=Sv0fKeRqtYgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=edf1wS77AAAA:8 a=hSkVLCK3AAAA:8 a=McGmopZ3JXA0FyUL-jwA:9 a=CjuIK1q_8ugA:10 a=kVLQuquJ2CynHSLU3hYA:9 a=a_PwQJl-kcHnX1M80qC6:22 a=DcSpbTIhAlouE1Uv7lRv:22 a=cQPPKAXgyycSBL8etih5:22 X-Proofpoint-ORIG-GUID: 4zJDCQqzoJLLU0nvCx2mSoie_vTdlG6h X-Proofpoint-Spam-Info: AW1haW4tMjYwODI0MDA4NyBTYWx0ZWRfXyN3crNVkzPoH 8kyAHeDfqHhVtf8Jcg1/X6b6k0E8YyOv97PT8/2dxsJUqAEbgqrIPf9lXyUIjE2Kst9YsbxsRM6 rgVFAqdyKc6H0ib/ZuemJ7nUkxPL5dw= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-24_03,2026-08-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 malwarescore=0 adultscore=0 lowpriorityscore=0 suspectscore=0 impostorscore=0 phishscore=0 spamscore=0 clxscore=1011 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608240087 --upSIBUhSliXFFaM1 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > bpf_xdp_shrink_data() frees a released frag via __xdp_return() using > xdp->rxq->mem.type, but that type is wrong for skb-backed XDP: the skb is > cow'd into page_pool memory while the rxq still says MEM_TYPE_PAGE_SHARED, > so the page_pool page is freed with page_frag_free() and we hit > "Bad page state ... page_pool leak". >=20 > Both generic XDP and veth are affected. A non-linear skb is cow'd into > page_pool memory (skb_cow_data_for_xdp() -> skb_pp_cow_data() for generic > XDP, veth_convert_skb_to_xdp_buff() for veth), so its frags become > page_pool pages while the rxq keeps MEM_TYPE_PAGE_SHARED. >=20 > We can't just fix rxq->mem.type in place: > - generic XDP: xdp->rxq is dev->_rx[queue].xdp_rxq (see > bpf_prog_run_generic_xdp()), a shared rxq that other CPUs may access in > parallel, so we must not write to it. > - veth: rq->xdp_rxq.mem is shared per-queue state that veth resets on XDP > teardown, and with GRO that reset runs without stopping in-flight NAPI, > so a type stashed there can be clobbered under a packet still in flight. >=20 > Adding a check in __xdp_return() or bpf_xdp_shrink_data() itself is not an > option either: without recording it somewhere, both can only guess the > frag's memory type, which quickly gets confusing. >=20 > So record it in the xdp_buff. Add a XDP_FLAGS_FRAGS_PAGE_POOL flag; the t= wo > skb-cow sites set it, and bpf_xdp_shrink_data() frees the frag to the > page_pool when it is set, otherwise it keeps falling back to > xdp->rxq->mem.type unchanged. No other path changes behaviour. >=20 > Fixes: e6d5dbdd20aa ("xdp: add multi-buff support for xdp running in gene= ric mode") > Fixes: 0ebab78cbcbf ("net: veth: add page_pool for page recycling") Hi Jiayuan Chen, thx for fixing it. Can we do something like the patch below instead? Regards, Lorenzo diff --git a/net/core/xdp.c b/net/core/xdp.c index 1d679e8fd649..4ed659b58141 100644 --- a/net/core/xdp.c +++ b/net/core/xdp.c @@ -433,16 +433,16 @@ EXPORT_SYMBOL_GPL(xdp_rxq_info_attach_page_pool); void __xdp_return(netmem_ref netmem, enum xdp_mem_type mem_type, bool napi_direct, struct xdp_buff *xdp) { + netmem_ref head_netmem =3D netmem_compound_head(netmem); + if (netmem_is_pp(head_netmem)) + mem_type =3D MEM_TYPE_PAGE_POOL; + switch (mem_type) { case MEM_TYPE_PAGE_POOL: - netmem =3D netmem_compound_head(netmem); if (napi_direct && xdp_return_frame_no_direct()) napi_direct =3D false; - /* No need to check netmem_is_pp() as mem->type knows this a - * page_pool page - */ - page_pool_put_full_netmem(netmem_get_pp(netmem), netmem, - napi_direct); + page_pool_put_full_netmem(netmem_get_pp(head_netmem), + head_netmem, napi_direct); break; case MEM_TYPE_PAGE_SHARED: page_frag_free(__netmem_address(netmem)); > Reported-by: syzbot+237bbeed8dfe0699b7f5@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=3D237bbeed8dfe0699b7f5 > Signed-off-by: Jiayuan Chen > --- > drivers/net/veth.c | 5 +++++ > include/net/xdp.h | 14 ++++++++++++++ > net/core/dev.c | 5 +++++ > net/core/filter.c | 7 +++++++ > 4 files changed, 31 insertions(+) >=20 > diff --git a/drivers/net/veth.c b/drivers/net/veth.c > index 6ed3ee81153f..0afa0661ada1 100644 > --- a/drivers/net/veth.c > +++ b/drivers/net/veth.c > @@ -775,6 +775,11 @@ static int veth_convert_skb_to_xdp_buff(struct veth_= rq *rq, > if (skb_shinfo(skb)->nr_frags) { > skb_shinfo(skb)->xdp_frags_size =3D skb->data_len; > xdp_buff_set_frags_flag(xdp); > + /* A nonlinear skb was cow'd into rq->page_pool above, so the > + * frags must be freed to that pool, not via the rxq's > + * MEM_TYPE_PAGE_SHARED. > + */ > + xdp_buff_set_frag_pp(xdp); > } else { > xdp_buff_clear_frags_flag(xdp); > } > diff --git a/include/net/xdp.h b/include/net/xdp.h > index aa742f413c35..b389dc527adc 100644 > --- a/include/net/xdp.h > +++ b/include/net/xdp.h > @@ -81,6 +81,10 @@ enum xdp_buff_flags { > * XDP program is not attached. > */ > XDP_FLAGS_FRAGS_UNREADABLE =3D BIT(2), > + /* frags are page_pool memory even though rxq->mem.type is not: a > + * skb-backed XDP buff (generic XDP, veth) is cow'd into a page_pool. > + */ > + XDP_FLAGS_FRAGS_PAGE_POOL =3D BIT(3), > }; > =20 > struct xdp_buff { > @@ -131,6 +135,16 @@ static __always_inline void xdp_buff_set_frag_unread= able(struct xdp_buff *xdp) > xdp->flags |=3D XDP_FLAGS_FRAGS_UNREADABLE; > } > =20 > +static __always_inline void xdp_buff_set_frag_pp(struct xdp_buff *xdp) > +{ > + xdp->flags |=3D XDP_FLAGS_FRAGS_PAGE_POOL; > +} > + > +static __always_inline bool xdp_buff_is_frag_pp(const struct xdp_buff *x= dp) > +{ > + return !!(xdp->flags & XDP_FLAGS_FRAGS_PAGE_POOL); > +} > + > static __always_inline u32 xdp_buff_get_skb_flags(const struct xdp_buff = *xdp) > { > return xdp->flags; > diff --git a/net/core/dev.c b/net/core/dev.c > index 38336858c168..be36020484b6 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -5532,6 +5532,11 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, = struct xdp_buff *xdp, > if (skb_is_nonlinear(skb)) { > skb_shinfo(skb)->xdp_frags_size =3D skb->data_len; > xdp_buff_set_frags_flag(xdp); > + /* A nonlinear skb was cow'd into page_pool memory by > + * skb_cow_data_for_xdp() before we got here, so the frags must > + * be freed to that pool, not via the rxq's MEM_TYPE_PAGE_SHARED. > + */ > + xdp_buff_set_frag_pp(xdp); > } else { > xdp_buff_clear_frags_flag(xdp); > } > diff --git a/net/core/filter.c b/net/core/filter.c > index 61940e753552..d34ba56d79d8 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -4378,6 +4378,13 @@ static bool bpf_xdp_shrink_data(struct xdp_buff *x= dp, skb_frag_t *frag, > if (mem_type =3D=3D MEM_TYPE_XSK_BUFF_POOL) { > netmem =3D 0; > zc_frag =3D bpf_xdp_shrink_data_zc(xdp, shrink, tail, release); > + } else if (xdp_buff_is_frag_pp(xdp)) { > + /* > + * Skb-backed XDP (generic XDP, veth) cow's the frags into a > + * page_pool while the rxq stays MEM_TYPE_PAGE_SHARED, so free > + * the frag to the pool, not via page_frag_free(). > + */ > + mem_type =3D MEM_TYPE_PAGE_POOL; > } > =20 > if (release) { > --=20 > 2.43.0 >=20 --upSIBUhSliXFFaM1 Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTquNwa3Txd3rGGn7Y6cBh0uS2trAUCaowdegAKCRA6cBh0uS2t rJGbAP0TKzr2n3NCwgiDdeslVGC7scK/HYqht13htuRgE0ixHAEAwIsqgO3mN1D9 7ii7J90tRRebrB44+8j3U937MKgYjwQ= =6sj/ -----END PGP SIGNATURE----- --upSIBUhSliXFFaM1--