[PATCH v5 8/9] platform/x86: hp-bioscfg: NUL-terminate the SPM auth token

[Muhammad Bilal <meatuni001@gmail.com>]

auth_token_store() copies the token with kmemdup(), which does not NUL
terminate it, but hp_calculate_security_buffer() and
hp_populate_security_buffer() use it as a C string and read past the
allocation.

A lone newline (echo > auth_token) is worse: kmemdup() of 0 bytes
returns ZERO_SIZE_PTR, which passes the NULL checks, so a later
attribute write passes it to strlen().

A userspace replica of the two helpers under ASan reports a heap
buffer overflow in hp_calculate_security_buffer() for the unterminated
token and a fault at address 0x10 for the lone newline, and is clean
with this change.

The token is a string, so copy it with kstrndup(), which always NUL
terminates and allocates at least one byte.

Fixes: b2715aa2e135 ("platform/x86: hp-bioscfg: spmobj-attributes")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
Changes in v5:
 drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c b/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
index 25477ecf8822..598bf3e1260e 100644
--- a/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
+++ b/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
@@ -317,7 +317,7 @@ static ssize_t auth_token_store(struct kobject *kobj,
 		length--;
 
 	/* allocate space and copy current auth token */
-	bioscfg_drv.spm_data.auth_token = kmemdup(buf, length, GFP_KERNEL);
+	bioscfg_drv.spm_data.auth_token = kstrndup(buf, length, GFP_KERNEL);
 	if (!bioscfg_drv.spm_data.auth_token) {
 		ret = -ENOMEM;
 		goto exit_token;
-- 
2.55.0