tcp: reject net_iov in zerocopy receive mapping hints

Overview

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

tcp: reject net_iov in zerocopy receive mapping hints

After copying a readable prefix, receive_fallback_to_copy() asks tcp_zerocopy_set_hint_for_skb() where page mapping can resume. If the next skb is unreadable, find_next_mappable_frag() passes its net_iov fragment to can_map_frag().

skb_frag_page() returns NULL for a net_iov, but can_map_frag() dereferences it in PageCompound(). A v7.2 KASAN run on a connected TCP socket with 64 readable bytes followed by a 4096-byte NET_IOV_DMABUF fragment reported:

BUG: KASAN: null-ptr-deref in can_map_frag tcp_zerocopy_receive -> can_map_frag Kernel panic - not syncing: KASAN: panic_on_warn set

The diagnostic inserted the net_iov directly because the test host has no devmem-capable NIC. Hardware end-to-end reachability remains untested and requires CONFIG_NET_DEVMEM plus a supported DMA-buf-bound RX queue.

Reject all net_iov fragments before skb_frag_page(). This covers both DMABUF and IOURING net_iov types while leaving page-backed checks unchanged. With the guard, the same queue copied the readable prefix, returned a 4096-byte skip hint, and completed without a fault.

Affected

• Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 563d3564513496b9ce3b3ba7a5154427554d0f06
• Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 1c7463ac0e99cc91c4eecc1b69a740ef1a619932
• Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 3aa6f536a95eb0617c313ae2eb76fdfa85331f85
• Linux >= 9f6b619edf2e85746f261b42ae8f818a59d126f7 < 8b1f0af1fd5fd113432233ed8a3862ee7c30a84f
• Linux 6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.