Linux Kernel Traffic Control (tc) Vulnerability Rated 7.8 CVSS

Status: UPDATED  |  Advisory ID: CVE-2026-74674

Key Details

Affected Products, Subsystems & Sectors

What to Know

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

mm: fix incorrect flush address in direct page table reclaim

When zap_pte_range reclaims a page table, it does:

pte_free_tlb(tlb, pmd_pgtable(pmdval), addr);

and this is unconditionally wrong: if this code executes, addr *always*

points one past the end of the range covered by the table. The addr

parameter is used to flush the TLB (really the paging-structure-cache)

to drop references to the to-be-freed table, and any architecture that

cares about the parameter will flush the wrong address. (But they'll

still free the correct page).

I think it's worth contemplating why the kernel works at all.

If we hit the offending line of code, we will first clear the PMD entry

(line 1954, zap_empty_pte_table), then we will issue pending flushes if

force_flush is set (tlb_flush_mmu_tlbonly(tlb)), then we will skip the

retry on line 1979 (phew!), and then we will do the offending

pte_free_tlb call. *Or* we will clear the PMD entry immediately before

pte_free_tlb (line 1983, zap_pte_table_if_empty).

If we have any pending flushes (i.e. we actually zapped any last-level

entries) at the time we clear the PMD entry, then the flush really ought

to flush all references to the table (Linus certainly seems to think it

will on all architectures [0]).

The condition under which we have no accumulated flushes at the time of

the clear is very complex (the whole zap_pte_range function has absurdly

complex control flow). If we do hit the bad case, then we will end up

clearing the PMD entry after the last time the range is flushed, and any

CPU is free to cache a reference to the (empty) page table. If this

happens due to an ordinary read or write, it would segfault, so it would

be rare. But the cache could be speculatively filled as well. Then

we'll flush the wrong address and then free and possibly reuse the

table.

On x86, even flushing the wrong address works on non-KPTI Intel systems

because INVLPG flushes *all* paging-structure-caches, not just the ones

for the target address. But INVPCID does not, and flush_tlb_one_user

will use INVPCID if it's available. And then we're toast. AMD systems

are more susceptible: we set the EFER.TCE bit, which makes even INVLPG

only flush the target address.

I think this might fix an issue in ripgrep reported here:

https://github.com/BurntSushi/ripgrep/issues/3494

[0] https://lore.kernel.org/all/CA+55aFzBggoXtNXQeng5d_mRoDnaMBE5Y+URs+PHR67nUpMtaw@mail.gmail.com/T/#u (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References