drm/amd/display: Fix buffer overflow in 'get_host_router_total_dp_tunnel_bw()'

The error message buffer overflow 'dc->links' 12 <= 12 suggests that the
code is trying to access an element of the dc->links array that is
beyond its bounds. In C, arrays are zero-indexed, so an array with 12
elements has valid indices from 0 to 11. Trying to access dc->links[12]
would be an attempt to access the 13th element of a 12-element array,
which is a buffer overflow.

To fix this, ensure that the loop does not go beyond the last valid
index when accessing dc->links[i + 1] by subtracting 1 from the loop
condition.

This would ensure that i + 1 is always a valid index in the array.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_dpia_bw.c:208 get_host_router_total_dp_tunnel_bw() error: buffer overflow 'dc->links' 12 <= 12

Fixes: 59f1622 ("drm/amd/display: Add dpia display mode validation logic")
Cc: PeiChen Huang <[email protected]>
Cc: Aric Cyr <[email protected]>
Cc: Rodrigo Siqueira <[email protected]>
Cc: Aurabindo Pillai <[email protected]>
Cc: Meenakshikumar Somasundaram <[email protected]>
Signed-off-by: Srinivasan Shanmugam <[email protected]>
Reviewed-by: Tom Chung <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: srishanm

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c

@@ -196,7 +196,7 @@ static int get_host_router_total_dp_tunnel_bw(const struct dc *dc, uint8_t hr_in
 	struct dc_link *link_dpia_primary, *link_dpia_secondary;
 	int total_bw = 0;
 
-	for (uint8_t i = 0; i < MAX_PIPES * 2; ++i) {
+	for (uint8_t i = 0; i < (MAX_PIPES * 2) - 1; ++i) {
 
 		if (!dc->links[i] || dc->links[i]->ep_type != DISPLAY_ENDPOINT_USB4_DPIA)
 			continue;