CVE-2026-43465

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

net/mlx5e: RX, Fix XDP multi-buf frag counting for striding 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.

The issue was discovered by the drivers/net/xdp.py selftest,

more specifically the test_xdp_native_tx_mb:

- The mlx5 driver allocates a page_pool page and initializes it with

a frag counter of 64 (pp_ref_count=64) and the internal frag counter

to 0.

- The test sends one packet with no payload.

- On RX (mlx5e_skb_from_cqe_mpwrq_nonlinear()), mlx5 configures the XDP

buffer with the packet data starting in the first fragment which is the

page mentioned above.

- The XDP program runs and calls bpf_xdp_pull_data() which moves the

header into the linear part of the XDP buffer. As the packet doesn't

contain more data, the program drops the tail fragment since it no

longer contains any payload (pp_ref_count=63).

- mlx5 device skips counting this fragment. Internal frag counter

remains 0.

- mlx5 releases all 64 fragments of the page but page pp_ref_count is

63 => negative reference counting error.

Resulting splat during the test:

WARNING: CPU: 0 PID: 188225 at ./include/net/page_pool/helpers.h:297 mlx5e_page_release_fragmented.isra.0+0xbd/0xe0 [mlx5_core]

Modules linked in: [...]

CPU: 0 UID: 0 PID: 188225 Comm: ip Not tainted 6.18.0-rc7_for_upstream_min_debug_2025_12_08_11_44 #1 NONE

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014

RIP: 0010:mlx5e_page_release_fragmented.isra.0+0xbd/0xe0 [mlx5_core]

[...]

Call Trace:

<TASK>

mlx5e_free_rx_mpwqe+0x20a/0x250 [mlx5_core]

mlx5e_dealloc_rx_mpwqe+0x37/0xb0 [mlx5_core]

mlx5e_free_rx_descs+0x11a/0x170 [mlx5_core]

mlx5e_close_rq+0x78/0xa0 [mlx5_core]

mlx5e_close_queues+0x46/0x2a0 [mlx5_core]

mlx5e_close_channel+0x24/0x90 [mlx5_core]

mlx5e_close_channels+0x5d/0xf0 [mlx5_core]

mlx5e_safe_switch_params+0x2ec/0x380 [mlx5_core]

mlx5e_change_mtu+0x11d/0x490 [mlx5_core]

mlx5e_change_nic_mtu+0x19/0x30 [mlx5_core]

netif_set_mtu_ext+0xfc/0x240

do_setlink.isra.0+0x226/0x1100

rtnl_newlink+0x7a9/0xba0

rtnetlink_rcv_msg+0x220/0x3c0

netlink_rcv_skb+0x4b/0xf0

netlink_unicast+0x255/0x380

netlink_sendmsg+0x1f3/0x420

__sock_sendmsg+0x38/0x60

____sys_sendmsg+0x1e8/0x240

___sys_sendmsg+0x7c/0xb0

[...]

__sys_sendmsg+0x5f/0xb0

do_syscall_64+0x55/0xc70

The problem applies for XDP_PASS as well which is handled in a different

code path in the driver.

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.