Re: [PATCH net v2] xsk: fix NULL pointer dereference in __xsk_rcv()
From: Jason Xing <hidden>
Date: 2026-07-25 09:14:11
Also in:
bpf, lkml
On Sat, Jul 25, 2026 at 11:43 AM Cen Zhang (Microsoft) [off-list ref] wrote:
In the __xsk_rcv() multi-buffer path, xsk_buff_alloc() is called in a
loop without checking its return value. xsk_buff_can_alloc() only
counts fill queue entries without validating their addresses, so it
can succeed while xsk_buff_alloc() rejects all remaining entries and
returns NULL.
Oops: general protection fault, probably for non-canonical address
0xdffffc0000000000
KASAN: null-ptr-deref in range
[0x0000000000000000-0x0000000000000007]
RIP: 0010:__xsk_rcv+0x426/0xc20 (net/xdp/xsk.c:350)
Call Trace:
xsk_generic_rcv+0x26d/0x5f0
xdp_do_generic_redirect+0x3c5/0xcf0
do_xdp_generic+0x92f/0xe70
__netif_receive_skb_core.constprop.0+0xf7e/0x2b30
Fix this with a two-stage transaction. First allocate and stage all
buffers required for the packet, recycling all staged buffers with
xsk_buff_free() if any allocation fails. Only after this stage
succeeds, copy the data, reserve the RX descriptors, and release the
buffers in an error-free loop.
Fixes: 804627751b42 ("xsk: add support for AF_XDP multi-buffer on Rx path")
Reported-by: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Cen Zhang (Microsoft) <redacted>You sent two patches within 24 hour, which obeys the basic rule of the netdev community. Please wait. Thanks, Jason
quoted hunk ↗ jump to hunk
--- v2: - Allocate all packet buffers before reserving RX descriptors. - Recycle partially allocated buffers instead of only cancelling the RX producer reservations. Link: https://lore.kernel.org/netdev/20260724164719.99563-1-blbllhy@gmail.com (local) net/xdp/xsk.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-)diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index f906d51b6699..383fc2b1de48 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c@@ -298,9 +298,11 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len) u32 frame_size = __xsk_pool_get_rx_frame_size(xs->pool); void *copy_from = xsk_copy_xdp_start(xdp), *copy_to; u32 from_len, meta_len, rem, num_desc; - struct xdp_buff_xsk *xskb; + struct xdp_buff_xsk *xskb, *tmp; struct xdp_buff *xsk_xdp; + LIST_HEAD(xsk_buffs); skb_frag_t *frag; + u32 i; from_len = xdp->data_end - copy_from; meta_len = xdp->data - copy_from;@@ -343,23 +345,44 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len) frag = &sinfo->frags[0]; } + for (i = 0; i < num_desc; i++) { + xsk_xdp = xsk_buff_alloc(xs->pool); + if (!xsk_xdp) + goto err_alloc; + + xskb = container_of(xsk_xdp, struct xdp_buff_xsk, xdp); + if (unlikely(!list_empty(&xskb->list_node))) + goto err_alloc; + list_add_tail(&xskb->list_node, &xsk_buffs); + } + do { u32 to_len = frame_size + meta_len; u32 copied; - xsk_xdp = xsk_buff_alloc(xs->pool); + xskb = list_first_entry(&xsk_buffs, struct xdp_buff_xsk, + list_node); + list_del_init(&xskb->list_node); + xsk_xdp = &xskb->xdp; copy_to = xsk_xdp->data - meta_len; copied = xsk_copy_xdp(copy_to, ©_from, to_len, &from_len, &frag, rem); rem -= copied; - xskb = container_of(xsk_xdp, struct xdp_buff_xsk, xdp); __xsk_rcv_zc_safe(xs, xskb, copied - meta_len, rem ? XDP_PKT_CONTD : 0); meta_len = 0; } while (rem); return 0; + +err_alloc: + list_for_each_entry_safe(xskb, tmp, &xsk_buffs, list_node) { + list_del_init(&xskb->list_node); + xsk_buff_free(&xskb->xdp); + } + xs->rx_dropped++; + return -ENOMEM; } static bool xsk_tx_writeable(struct xdp_sock *xs) --2.53.0