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

[SHANMUGAM, SRINIVASAN]

[AMD Official Use Only - General]



From: SHANMUGAM, SRINIVASAN
Sent: Tuesday, January 30, 2024 3:18 PM
To: Siqueira, Rodrigo <Rodrigo.Siqueira at amd.com>; Pillai, Aurabindo <Aurabindo.Pillai at amd.com>
Cc: Cyr, Aric <Aric.Cyr at amd.com>; amd-gfx at lists.freedesktop.org; Somasundaram, Meenakshikumar <Meenakshikumar.Somasundaram at amd.com>; Huang, PeiChen (Pei-Chen) <PeiChen.Huang at amd.com>
Subject: Re: [PATCH] drm/amd/display: Fix buffer overflow in 'get_host_router_total_dp_tunnel_bw()'


+ Cc: Tom Chung <chiahsuan.chung at amd.com<mailto:chiahsuan.chung at amd.com>>
On 1/29/2024 9:19 PM, Srinivasan Shanmugam wrote:

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: 9ed0893b7c58 ("drm/amd/display: Add dpia display mode validation logic")

Cc: PeiChen Huang <peichen.huang at amd.com><mailto:peichen.huang at amd.com>

Cc: Aric Cyr <aric.cyr at amd.com><mailto:aric.cyr at amd.com>

Cc: Rodrigo Siqueira <rodrigo.siqueira at amd.com><mailto:rodrigo.siqueira at amd.com>

Cc: Aurabindo Pillai <aurabindo.pillai at amd.com><mailto:aurabindo.pillai at amd.com>

Cc: Meenakshikumar Somasundaram <meenakshikumar.somasundaram at amd.com><mailto:meenakshikumar.somasundaram at amd.com>

Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com><mailto:srinivasan.shanmugam at amd.com>

---

 drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)



diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c

index dd0d2b206462..5491b707cec8 100644

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

+++ b/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;
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