On 9/13/26 9:05 PM, Lorenzo Bianconi wrote:
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. A dedicated mem_type field (mirroring
xdp_frame->mem_type) would read more naturally, but it grows xdp_buff, and
struct xdp_page_head embeds two of them, which shifts the layout the
xdp_do_redirect live-frames selftest hard-codes (MAX_PKT_SIZE). So use a
flag bit: add XDP_FLAGS_FRAGS_PAGE_POOL, 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.
I have not looked into the details yet, but I am wondering if it is possible
to just move xdp_mem_info type (or ever the full xdp_mem_info) in xdp_buff and
remove it from xdp_rxq_info struct. What do you think?
I think that would read better, but it touches ~20 datapath sites plus a
few drivers, so I choose keeping this one small enough to backport.
The flag describes the buff, so the buff <-> frame conversions have to keep
it consistent:
- buff -> frame: xdp_update_frame_from_buff() copies xdp->flags into the
frame. veth XDP_TX/XDP_REDIRECT hand the frame to the peer, and cpumap
and devmap run a second program on it, so the peer would inherit a stale
tag; strip it, an xdp_frame describes its memory with ::mem_type.
- frame -> buff: xdp_convert_frame_to_buff() rebuilds a buff, and veth and
devmap then run a program whose rxq says MEM_TYPE_PAGE_SHARED even for a
page_pool frame (only cpumap copies mem_type into the rxq). A shrink
there leaks the same way (this predates the series: bpf_xdp_adjust_tail()
frees frags by rxq->mem.type), so re-derive the flag from the frame's
::mem_type.
Fixes: e6d5dbdd20aa ("xdp: add multi-buff support for xdp running in generic
mode")
Fixes: 0ebab78cbcbf ("net: veth: add page_pool for page recycling")
Fixes: bf25146a5595 ("bpf: add frags support to the bpf_xdp_adjust_tail() API")
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=237bbeed8dfe0699b7f5
Signed-off-by: Jiayuan Chen <[email protected]>
---
drivers/net/veth.c | 6 ++++++
include/net/xdp.h | 30 +++++++++++++++++++++++++++++-
net/core/dev.c | 6 ++++++
net/core/filter.c | 7 +++++++
4 files changed, 48 insertions(+), 1 deletion(-)
diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 6ed3ee81153fb..a3fdf1959b76c 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -775,6 +775,12 @@ 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);
Even if it is not a real problem at the moment, I still think we should
set it not just if we have a non-liner skb, but for all skb returned by
skb_pp_cow_data().
It's not an actual problem today, so I won't respin just for this, but
I'll fold it in if there is a v4.
} else {
xdp_buff_clear_frags_flag(xdp);
}
diff --git a/include/net/xdp.h b/include/net/xdp.h
index aa742f413c358..8fd4139e9cbd3 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -81,6 +81,14 @@ 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_buff only: an xdp_frame describes its memory with ::mem_type, so
+ * this is stripped in xdp_update_frame_from_buff() and re-derived from
+ * ::mem_type in xdp_convert_frame_to_buff().
+ */
+ XDP_FLAGS_FRAGS_PAGE_POOL = BIT(3),
};
struct xdp_buff {
@@ -131,6 +139,16 @@ 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;
@@ -394,6 +412,15 @@ void xdp_convert_frame_to_buff(const struct xdp_frame
*frame,
xdp->data_meta = frame->data - frame->metasize;
xdp->frame_sz = frame->frame_sz;
xdp->flags = frame->flags;
+ /*
+ * frame->flags never carries XDP_FLAGS_FRAGS_PAGE_POOL (it is stripped
+ * in xdp_update_frame_from_buff()); re-derive it from the frame's own
+ * memory type. veth and devmap rebuild a buff here and run a program
+ * whose rxq says MEM_TYPE_PAGE_SHARED, so without this a shrink would
+ * free a page_pool frag through page_frag_free().
+ */
+ if (frame->mem_type == MEM_TYPE_PAGE_POOL)
+ xdp_buff_set_frag_pp(xdp);
}
static inline
@@ -420,7 +447,8 @@ int xdp_update_frame_from_buff(const struct xdp_buff *xdp,
xdp_frame->headroom = headroom - sizeof(*xdp_frame);
xdp_frame->metasize = metasize;
xdp_frame->frame_sz = xdp->frame_sz;
- xdp_frame->flags = xdp->flags;
+ /* XDP_FLAGS_FRAGS_PAGE_POOL is xdp_buff only, don't carry it over */
+ xdp_frame->flags = xdp->flags & ~XDP_FLAGS_FRAGS_PAGE_POOL;
IIUC this is only necessary for the veth case, right? If so, I would suggest to
move it in veth driver (or to have a helper function called just in veth).
Regards,
Lorenzo
Not only veth - cpumap and devmap call xdp_update_frame_from_buff() too,
and their buff came from xdp_convert_frame_to_buff(), which sets the bit
from frame->mem_type.
Without the strip it bites via xdpf_clone() (devmap broadcast):
memcpy(addr, xdpf, totalsize); /* copies flags as is */
nxdpf->mem_type = MEM_TYPE_PAGE_ORDER0; /* flags left alone */
the clone ends up ORDER0 with the page_pool bit still set, so the next
xdp_convert_frame_to_buff() hands the prog a buff claiming page_pool
over an ORDER0 page.
