CVE-2026-64113: ixgbevf: fix use-after-free in VEPA multicast source pruning

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

ixgbevf: fix use-after-free in VEPA multicast source pruning

ixgbevfcleanrxirq() prunes frames whose source MAC matches the VF's own address (VEPA multicast workaround) by freeing the skb and continuing to the next descriptor:

devkfreeskbirq(skb); continue;

The skb pointer is declared outside the while loop and persists across iterations. Because the continue skips the "skb = NULL" reset at the bottom of the loop, the next iteration enters the "else if (skb)" path and calls ixgbevfaddrxfrag() on the freed skb, dereferencing skbshinfo(skb)->nrfrags - a use-after-free in NAPI softirq context.

The sibling driver iavf already handles this correctly by nulling the pointer before continuing. Apply the same pattern here.

I do not have ixgbevf hardware; the bug was found by static analysis (scandropcontinueloops.py + semgrep dropcontinueinloop, multi-tool corroboration with the highest score in the scan). The UAF was confirmed under KASAN by loading a test module that reproduces the exact code pattern (alloc skb, kfreeskb, then read skbshinfo(skb)->nrfrags):

BUG: KASAN: slab-use-after-free in ixgbevfuaftestinit+0x100/0x1000 Read of size 8 at addr 000000006163ae78 by task insmod/30 freed 208-byte region [000000006163adc0, 000000006163ae90)

QEMU emulates igb (82576) but not ixgbe (82599), and the igbvf VF driver does not include the VEPA source pruning path, so a full end-to-end reproduction with emulated hardware was not possible.