[PATCH v5 6/9] platform/x86: hp-bioscfg: fix heap OOB in hp_enforce_single_line_input()

[Muhammad Bilal <meatuni001@gmail.com>]

The store handlers copy the input with kstrdup(), which stops at the
first NUL, but pass the full write size to
hp_enforce_single_line_input(). With an embedded NUL the copy is
shorter than count, so the helper reads, and can write one byte, past
the allocation.

Writing "A\0" followed by 4093 bytes of "B" to current_password makes
memchr() scan 4093 bytes past a 2-byte copy. On an HP EliteBook 840 G2
running Linux 7.2.7 all 100 such writes fail with -EINVAL although the
input has no newline, so memchr() matched one in the heap. A userspace
replica of the helper under ASan reports a 4095 byte read, 0 bytes
after the 2-byte region, and is clean with this change.

The input is a string, so only scan up to its first NUL.

Fixes: a34fc329b189 ("platform/x86: hp-bioscfg: bioscfg")
Cc: stable@vger.kernel.org
Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
Changes in v5:
 drivers/platform/x86/hp/hp-bioscfg/bioscfg.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/platform/x86/hp/hp-bioscfg/bioscfg.c b/drivers/platform/x86/hp/hp-bioscfg/bioscfg.c
index 754ab03bfd7b..84d75926d768 100644
--- a/drivers/platform/x86/hp/hp-bioscfg/bioscfg.c
+++ b/drivers/platform/x86/hp/hp-bioscfg/bioscfg.c
@@ -166,6 +166,8 @@ int hp_enforce_single_line_input(char *buf, size_t count)
 {
 	char *p;
 
+	/* buf is a string, ignore anything after its first NUL */
+	count = strnlen(buf, count);
 	p = memchr(buf, '\n', count);
 
 	if (p == buf + count - 1)
-- 
2.55.0