[PATCH v2 2/9] platform/x86: hp-bioscfg: fix heap OOB read in sk_store and kek_store

sk_store() and kek_store() strip a trailing newline from the sysfs
write before allocating the key buffer:

	length = count;
	if (buf[length - 1] == '\n')
		length--;
	bioscfg_drv.spm_data.signing_key = kmemdup(buf, length, GFP_KERNEL);

but then pass the original "count" (not "length") as the copy size to
hp_wmi_perform_query(), which memcpy()s that many bytes out of the
"length"-sized allocation, reading one byte past it whenever the write
ends in a newline, the normal case for a shell "echo" into sysfs.

KASAN confirms this directly:

  BUG: KASAN: slab-out-of-bounds in hp_wmi_perform_query+0x1e9/0x460 [hp_bioscfg]
  Read of size 28 at addr ffff88813c8e2b80 by task python3/16022
  ...
  sk_store+0xa7/0x240 [hp_bioscfg]
  kernfs_fop_write_iter+0x3e1/0x5d0
  ...
  The buggy address is located 0 bytes inside of
  allocated 27-byte region [ffff88813c8e2b80, ffff88813c8e2b9b)

Reproduced identically for kek_store, and at multiple write sizes
(28, 57, 201 bytes), each time reading exactly one byte past a
kmemdup() allocation one byte smaller than the write.

Fix by passing "length" instead of "count" to hp_wmi_perform_query()
in both functions.

Fixes: b2715aa2e135 ("platform/x86: hp-bioscfg: spmobj-attributes")
Cc: [email protected]
Signed-off-by: Muhammad Bilal <[email protected]>
---
 drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c b/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
index 2b00a14792e9..4d94e48c1a4c 100644
--- a/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
+++ b/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
@@ -238,7 +238,7 @@ static ssize_t sk_store(struct kobject *kobj,
 	ret = hp_wmi_perform_query(HPWMI_SECUREPLATFORM_SET_SK,
 				   HPWMI_SECUREPLATFORM,
 				   (void *)bioscfg_drv.spm_data.signing_key,
-				   count, 0);
+				   length, 0);
 
 	if (!ret) {
 		bioscfg_drv.spm_data.mechanism = SIGNING_KEY;
@@ -274,7 +274,7 @@ static ssize_t kek_store(struct kobject *kobj,
 	ret = hp_wmi_perform_query(HPWMI_SECUREPLATFORM_SET_KEK,
 				   HPWMI_SECUREPLATFORM,
 				   (void *)bioscfg_drv.spm_data.endorsement_key,
-				   count, 0);
+				   length, 0);
 
 	if (!ret) {
 		bioscfg_drv.spm_data.mechanism = ENDORSEMENT_KEY;
-- 
2.55.0