> 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".
>
> 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.
>
> 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.
>
> 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.
>
> So record it in the xdp_buff. Add a XDP_FLAGS_FRAGS_PAGE_POOL flag; the two
> 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.
>
> Fixes: e6d5dbdd20aa ("xdp: add multi-buff support for xdp running in generic
> 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 = netmem_compound_head(netmem);
+ if (netmem_is_pp(head_netmem))
+ mem_type = MEM_TYPE_PAGE_POOL;
+
switch (mem_type) {
case MEM_TYPE_PAGE_POOL:
- netmem = netmem_compound_head(netmem);
if (napi_direct && xdp_return_frame_no_direct())
napi_direct = 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: [email protected]
> Closes: https://syzkaller.appspot.com/bug?extid=237bbeed8dfe0699b7f5
> Signed-off-by: Jiayuan Chen <[email protected]>
> ---
> 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(+)
>
> 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 = 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 = 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 = BIT(3),
> };
>
> struct xdp_buff {
> @@ -131,6 +135,16 @@ static __always_inline void
> xdp_buff_set_frag_unreadable(struct xdp_buff *xdp)
> xdp->flags |= XDP_FLAGS_FRAGS_UNREADABLE;
> }
>
> +static __always_inline void xdp_buff_set_frag_pp(struct xdp_buff *xdp)
> +{
> + xdp->flags |= XDP_FLAGS_FRAGS_PAGE_POOL;
> +}
> +
> +static __always_inline bool xdp_buff_is_frag_pp(const struct xdp_buff *xdp)
> +{
> + 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 = 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 *xdp,
> skb_frag_t *frag,
> if (mem_type == MEM_TYPE_XSK_BUFF_POOL) {
> netmem = 0;
> zc_frag = 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 = MEM_TYPE_PAGE_POOL;
> }
>
> if (release) {
> --
> 2.43.0
>
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