UBUNTU-CVE-2026-81013: Medium severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: platform/x86: hp-bioscfg: fix heap OOB read on empty password write validatepasswordinput() computes length = strlen(buf) and then checks buf[length - 1] to strip a trailing newline, without checking that length is nonzero first. Writing an empty string (a bare '\n') to currentpassword or newpassword gives length == 0, and buf[length - 1] reads buf[-1], one byte before the heap allocation holding the copied input. KASAN confirms this directly: BUG: KASAN: slab-out-of-bounds in storepasswordinstance.constprop.0+0x223/0x2a0 [hpbioscfg] Read of size 1 at addr ffff88811bd8da9f by task sh/13740 ... storepasswordinstance.constprop.0+0x223/0x2a0 [hpbioscfg] currentpasswordstore+0x14/0x20 [hpbioscfg] ... The buggy address is located 23 bytes to the right of allocated 8-byte region [ffff88811bd8da80, ffff88811bd8da88) Reproduced identically via newpasswordstore. Execution continues past the bad read (the garbage byte only affects whether "length" is decremented by one), so the write completes and returns success; this is a pure information read past the buffer, not a crash, but it is still an out-of-bounds access KASAN correctly flags. Fix by only checking buf[length - 1] when length is nonzero.