CVE-2026-43464

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: RX, Fix XDP multi-buf frag counting for legacy RQ

XDP multi-buf programs can modify the layout of the XDP buffer when the

program calls bpf_xdp_pull_data() or bpf_xdp_adjust_tail(). The

referenced commit in the fixes tag corrected the assumption in the mlx5

driver that the XDP buffer layout doesn't change during a program

execution. However, this fix introduced another issue: the dropped

fragments still need to be counted on the driver side to avoid page

fragment reference counting issues.

Such issue can be observed with the

test_xdp_native_adjst_tail_shrnk_data selftest when using a payload of

3600 and shrinking by 256 bytes (an upcoming selftest patch): the last

fragment gets released by the XDP code but doesn't get tracked by the

driver. This results in a negative pp_ref_count during page release and

the following splat:

WARNING: include/net/page_pool/helpers.h:297 at mlx5e_page_release_fragmented.isra.0+0x4a/0x50 [mlx5_core], CPU#12: ip/3137

Modules linked in: [...]

CPU: 12 UID: 0 PID: 3137 Comm: ip Not tainted 6.19.0-rc3+ #12 NONE

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014

RIP: 0010:mlx5e_page_release_fragmented.isra.0+0x4a/0x50 [mlx5_core]

[...]

Call Trace:

<TASK>

mlx5e_dealloc_rx_wqe+0xcb/0x1a0 [mlx5_core]

mlx5e_free_rx_descs+0x7f/0x110 [mlx5_core]

mlx5e_close_rq+0x50/0x60 [mlx5_core]

mlx5e_close_queues+0x36/0x2c0 [mlx5_core]

mlx5e_close_channel+0x1c/0x50 [mlx5_core]

mlx5e_close_channels+0x45/0x80 [mlx5_core]

mlx5e_safe_switch_params+0x1a5/0x230 [mlx5_core]

mlx5e_change_mtu+0xf3/0x2f0 [mlx5_core]

netif_set_mtu_ext+0xf1/0x230

do_setlink.isra.0+0x219/0x1180

rtnl_newlink+0x79f/0xb60

rtnetlink_rcv_msg+0x213/0x3a0

netlink_rcv_skb+0x48/0xf0

netlink_unicast+0x24a/0x350

netlink_sendmsg+0x1ee/0x410

__sock_sendmsg+0x38/0x60

____sys_sendmsg+0x232/0x280

___sys_sendmsg+0x78/0xb0

__sys_sendmsg+0x5f/0xb0

[...]

do_syscall_64+0x57/0xc50

This patch fixes the issue by doing page frag counting on all the

original XDP buffer fragments for all relevant XDP actions (XDP_TX ,

XDP_REDIRECT and XDP_PASS). This is basically reverting to the original

counting before the commit in the fixes tag.

As frag_page is still pointing to the original tail, the nr_frags

parameter to xdp_update_skb_frags_info() needs to be calculated

in a different way to reflect the new nr_frags.