[PATCH v4] drm/amdgpu: Fix snprintf buffer size in smu_v14_0_init_microcode

[Srinivasan Shanmugam]

This commit addresses buffer overflow in the smu_v14_0_init_microcode
function. The issue was about the snprintf function writing more bytes
into the fw_name buffer than it can hold.

The line of code is:

snprintf(fw_name, sizeof(fw_name), "amdgpu/%s.bin", ucode_prefix);

Here, snprintf is used to write a formatted string into fw_name. The
format is "amdgpu/%s.bin", where %s is a placeholder for the string
ucode_prefix. The sizeof(fw_name) argument tells snprintf the maximum
number of bytes it can write into fw_name, including the
null-terminating character. In the original code, fw_name is an array of
30 characters.

The string "amdgpu/%s.bin" could be up to 41 bytes long, which exceeds
the 30 bytes allocated for fw_name. This is because %s could be replaced
by ucode_prefix, which can be up to 29 characters long. Adding the 12
characters from "amdgpu/" and ".bin", the total length could be 41
characters.

To address this, the size of ucode_prefix has been reduced to 15
characters. This ensures that the maximum length of the string written
into fw_name does not exceed its capacity.

As smu_13/14 etc. don't follow legacy scheme ie.,
amdgpu_ucode_legacy_naming

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/../pm/swsmu/smu14/smu_v14_0.c: In function ‘smu_v14_0_init_microcode’:
drivers/gpu/drm/amd/amdgpu/../pm/swsmu/smu14/smu_v14_0.c:80:52: warning: ‘%s’ directive output may be truncated writing up to 29 bytes into a region of size 23 [-Wformat-truncation=]
   80 |         snprintf(fw_name, sizeof(fw_name), "amdgpu/%s.bin", ucode_prefix);
      |                                                    ^~       ~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../pm/swsmu/smu14/smu_v14_0.c:80:9: note: ‘snprintf’ output between 12 and 41 bytes into a destination of size 30
   80 |         snprintf(fw_name, sizeof(fw_name), "amdgpu/%s.bin", ucode_prefix);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: fe6cd9152464 ("drm/amd/swsmu: add smu14 ip support")
Cc: Li Ma <li.ma at amd.com>
Cc: Likun Gao <Likun.Gao at amd.com>
Cc: Lijo Lazar <lijo.lazar at amd.com>
Cc: Kenneth Feng <kenneth.feng at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Christian König <christian.koenig at amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
---
v4:
 - Reduced ucode_prefix to 15 instead of fw_name size increasing as
   smu_13/14 etc. don't follow legacy scheme ie.,
   amdgpu_ucode_legacy_naming (Lijo) 

 drivers/gpu/drm/amd/pm/swsmu/smu14/smu_v14_0.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/pm/swsmu/smu14/smu_v14_0.c b/drivers/gpu/drm/amd/pm/swsmu/smu14/smu_v14_0.c
index 7d2055b9d19f..68b9bf822e8d 100644
--- a/drivers/gpu/drm/amd/pm/swsmu/smu14/smu_v14_0.c
+++ b/drivers/gpu/drm/amd/pm/swsmu/smu14/smu_v14_0.c
@@ -65,7 +65,7 @@ int smu_v14_0_init_microcode(struct smu_context *smu)
 {
 	struct amdgpu_device *adev = smu->adev;
 	char fw_name[30];
-	char ucode_prefix[30];
+	char ucode_prefix[15];
 	int err = 0;
 	const struct smc_firmware_header_v1_0 *hdr;
 	const struct common_firmware_header *header;
-- 
2.34.1