Medium [CVE-2026-53199] use kmap_local_page in netvsc_copy_to_send_buf
This medium-severity Red Hat Linux advisory covers CVE-2026-53199 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
In the Linux kernel, the following vulnerability has been resolved: hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf netvsc_copy_to_send_buf() copies page buffer entries into the VMBus send buffer using phys_to_virt() on the entry PFN.
Entries for the RNDIS header and the skb linear data come from kmalloc'd memory and are always in the kernel direct map, but entries for skb fragments reference page cache or user pages, which on 32-bit x86 with CONFIG_HIGHMEM=y can live above the LOWMEM boundary.
For such a page phys_to_virt() returns an address outside the direct map and the subsequent memcpy() faults on the transmit softirq path, which is fatal. Map the pages with kmap_local_page() instead, handling two properties of the page buffer entries: - pb[i].pfn is a Hyper-V PFN at HV_HYP_PAGE_SIZE (4K) granularity, not a native PFN.
Reconstruct the physical address first and derive the native page from it, so the mapping stays correct where PAGE_SIZE > HV_HYP_PAGE_SIZE (e.g. arm64 with 64K pages). - Since commit 41a6328b2c55 ("hv_netvsc: Preserve contiguous PFN grouping in the page buffer array"), an entry describes a full physically contiguous fragment and pb[i].len can exceed PAGE_SIZE, while kmap_local_page() maps a single page.
Copy page by page, splitting at native page boundaries.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 9 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 9 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 9 days ago·verify at source
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