In the Linux kernel, the following vulnerability has been resolved: platform/x86: hp-bioscfg: fix heap OOB read on empty password write va

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

platform/x86: hp-bioscfg: fix heap OOB read on empty password write

validate_password_input() 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 current_password or new_password 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 store_password_instance.constprop.0+0x223/0x2a0 [hp_bioscfg]
Read of size 1 at addr ffff88811bd8da9f by task sh/13740
...
store_password_instance.constprop.0+0x223/0x2a0 [hp_bioscfg]
current_password_store+0x14/0x20 [hp_bioscfg]
...
The buggy address is located 23 bytes to the right of
allocated 8-byte region [ffff88811bd8da80, ffff88811bd8da88)

Reproduced identically via new_password_store. 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.