[PATCH] drm/amd/display: Add checks to prevent buffer overflow in mod_hdcp_dump_binary_message

[Srinivasan Shanmugam]

This commit addresses a buffer overflow issue in the
mod_hdcp_dump_binary_message function in the display/hdcp module

The issue arises when the 'buf' pointer is NULL or the 'buf_pos' index
exceeds the 'buf_size', and is passed to the sprintf function, which
attempts to write to an invalid memory location. This is leading to
undefined behavior

To resolve this, checks are added to ensure that 'buf' is not NULL and
'buf_pos' is within the bounds of 'buf_size' before it is passed to the
sprintf function. This change prevents the buffer overflow.

Fixes the below:
In function ‘mod_hdcp_dump_binary_message’,
    inlined from ‘mod_hdcp_dump_binary_message’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:29:6,
    inlined from ‘mod_hdcp_log_ddc_trace’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:107:3:
drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:47:25: warning: null destination pointer [-Wformat-overflow=]
   47 |                         sprintf(&buf[buf_pos], "%02X ", msg[i]);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘mod_hdcp_dump_binary_message’,
    inlined from ‘mod_hdcp_dump_binary_message’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:29:6,
    inlined from ‘mod_hdcp_log_ddc_trace’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:122:3:
drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:47:25: warning: null destination pointer [-Wformat-overflow=]
   47 |                         sprintf(&buf[buf_pos], "%02X ", msg[i]);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘mod_hdcp_dump_binary_message’,
    inlined from ‘mod_hdcp_dump_binary_message’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:29:6,
    inlined from ‘mod_hdcp_log_ddc_trace’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:61:3:
drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:47:25: warning: null destination pointer [-Wformat-overflow=]
   47 |                         sprintf(&buf[buf_pos], "%02X ", msg[i]);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘mod_hdcp_dump_binary_message’,
    inlined from ‘mod_hdcp_dump_binary_message’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:29:6,
    inlined from ‘mod_hdcp_log_ddc_trace’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:70:3:
drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:47:25: warning: null destination pointer [-Wformat-overflow=]
   47 |                         sprintf(&buf[buf_pos], "%02X ", msg[i]);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘mod_hdcp_dump_binary_message’,
    inlined from ‘mod_hdcp_dump_binary_message’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:29:6,
    inlined from ‘mod_hdcp_log_ddc_trace’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:73:3:
drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:47:25: warning: null destination pointer [-Wformat-overflow=]
   47 |                         sprintf(&buf[buf_pos], "%02X ", msg[i]);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘mod_hdcp_dump_binary_message’,
    inlined from ‘mod_hdcp_dump_binary_message’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:29:6,
    inlined from ‘mod_hdcp_log_ddc_trace’ at drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:70:3:
drivers/gpu/drm/amd/amdgpu/../display/modules/hdcp/hdcp_log.c:47:25: warning: null destination pointer [-Wformat-overflow=]
   47 |                         sprintf(&buf[buf_pos], "%02X ", msg[i]);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Wenjing Liu <wenjing.liu at amd.com>
Cc: Tom Chung <chiahsuan.chung at amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira at amd.com>
Cc: Roman Li <roman.li at amd.com>
Cc: Hersen Wu <hersenxs.wu at amd.com>
Cc: Alex Hung <alex.hung at amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai at amd.com>
Cc: Harry Wentland <harry.wentland at amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
---
 drivers/gpu/drm/amd/display/modules/hdcp/hdcp_log.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_log.c b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_log.c
index 6b3b5f610907..285251711a2d 100644
--- a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_log.c
+++ b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_log.c
@@ -40,9 +40,9 @@ void mod_hdcp_dump_binary_message(uint8_t *msg, uint32_t msg_size,
 	uint32_t buf_pos = 0;
 	uint32_t i = 0;
 
-	if (buf_size >= target_size) {
+	if (buf_size >= target_size && buf) {
 		for (i = 0; i < msg_size; i++) {
-			if (i % bytes_per_line == 0)
+			if (i % bytes_per_line == 0 && buf_pos < buf_size)
 				buf[buf_pos++] = '\n';
 			sprintf(&buf[buf_pos], "%02X ", msg[i]);
 			buf_pos += byte_size;
-- 
2.34.1