[PATCH v2 5/9] platform/x86: hp-bioscfg: fix off-by-one heap OOB write in audit_log_entries_show

[Muhammad Bilal <meatuni001@gmail.com>]

The per-iteration guard in audit_log_entries_show() is:

	if (ret < 0 || (LOG_ENTRY_SIZE * i) > PAGE_SIZE)
		break;
	...
	memcpy(buf, audit_log_buffer, LOG_ENTRY_SIZE);
	buf += LOG_ENTRY_SIZE;

At i == 256 (PAGE_SIZE / LOG_ENTRY_SIZE), LOG_ENTRY_SIZE * i equals
PAGE_SIZE exactly, which is not ">" PAGE_SIZE, so the loop does not
break and instead writes another LOG_ENTRY_SIZE (16) bytes starting at
offset 4096 of the page-sized sysfs output buffer, one entry past its
end.

This needs the BIOS to report more than 256 audit log entries, which
already exceeds this driver's own documented LOG_MAX_ENTRIES of 254,
so it requires a non-compliant or corrupted firmware value rather than
the roughly 85 million entries an unrelated integer-overflow read of
this code might suggest.

Fix by checking the bound against the offset the write is about to
reach, (i + 1), instead of the offset already written.

Fixes: 63e8f906e94e ("platform/x86: hp-bioscfg: surestart-attributes")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
 drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c b/drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c
index b57e42f29282..6b63fdb84606 100644
--- a/drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c
+++ b/drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c
@@ -90,7 +90,7 @@ static ssize_t audit_log_entries_show(struct kobject *kobj,
 					   HPWMI_SURESTART,
 					   audit_log_buffer, 1, 128);
 
-		if (ret < 0 || (LOG_ENTRY_SIZE * i) > PAGE_SIZE) {
+		if (ret < 0 || (LOG_ENTRY_SIZE * (i + 1)) > PAGE_SIZE) {
 			/*
 			 * Encountered a failure while reading
 			 * individual logs. Only a partial list of
-- 
2.55.0