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

[Chung, ChiaHsuan (Tom)]

It looks good to me.

Reviewed-by: Tom Chung <chiahsuan.chung at amd.com> 
<mailto:chiahsuan.chung at amd.com>

On 1/30/2024 5:49 PM, SHANMUGAM, SRINIVASAN wrote:
>
> [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>
>
> 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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