CVE-2026-89436

Description

In the Linux kernel, the following vulnerability has been resolved: platform/x86: panasonic-laptop: Fix sentinel write past pcc->sinf[] acpi_pcc_retrieve_biosdata() rejects SINF packages only when pcc->num_sifr is strictly less than hkey->package.count, then unconditionally writes a trailing sentinel at pcc->sinf[hkey->package.count]. But pcc->sinf[] is allocated with exactly pcc->num_sifr elements (valid indices 0..num_sifr-1), so that write needs num_sifr strictly greater than package.count to stay in bounds -- num_sifr == package.count passes the existing check but still overflows by one element. This is exactly the case probe()'s existing num_sifr++ workaround ("Some DSDT-s have an off-by-one bug where the SINF package count is one higher than the SQTY reported value") is written to accommodate: when a DSDT's SINF package count equals SQTY+1, the workaround makes num_sifr equal to package.count, which is precisely the boundary that overflows here. Found via UBSan (array-index-out-of-bounds) on hardware where HKEY.SQTY returns 37 and HKEY.SINF()'s package has 38 elements: num_sifr becomes 38 after the += 1 workaround, the loop correctly fills indices 0..37, and the sentinel write then targets index 38, one past the end -- a silent 4-byte heap overflow on kernels without CONFIG_UBSAN. Tightening the rejection check to num_sifr <= package.count would avoid the overflow but breaks probe() entirely on exactly this hardware, since num_sifr == package.count is the case the off-by-one workaround exists to support. Nothing else in the driver reads this sentinel value back, so simply skip the write when there is no room for it instead.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://git.kernel.org/stable/c/329f10d8be193bf36af124e00b9dd6644cd71724
• https://git.kernel.org/stable/c/a93df956ee4d903735b6d395362c839cb1dc07e3