Re: [PATCH] EDAC, thunderx: fix possible out-of-bounds string access.

[Gustavo A. R. Silva]

On 11/22/23 16:19, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> Commit 1b56c90018f0 ("Makefile: Enable -Wstringop-overflow globally") exposes a
> warning for a common bug in the usage of strncat():

Great to see this catching bugs already. :)

> drivers/edac/thunderx_edac.c: In function 'thunderx_ocx_com_threaded_isr':
> drivers/edac/thunderx_edac.c:1136:17: error: 'strncat' specified bound 1024 equals destination size [-Werror=stringop-overflow=]
>   1136 |                 strncat(msg, other, OCX_MESSAGE_SIZE);
>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/edac/thunderx_edac.c:1145:33: error: 'strncat' specified bound 1024 equals destination size [-Werror=stringop-overflow=]
>   1145 |                                 strncat(msg, other, OCX_MESSAGE_SIZE);
>        |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/edac/thunderx_edac.c:1150:33: error: 'strncat' specified bound 1024 equals destination size [-Werror=stringop-overflow=]
>   1150 |                                 strncat(msg, other, OCX_MESSAGE_SIZE);
>        |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/edac/thunderx_edac.c: In function 'thunderx_l2c_threaded_isr':
> drivers/edac/thunderx_edac.c:1899:17: error: 'strncat' specified bound 1024 equals destination size [-Werror=stringop-overflow=]
>   1899 |                 strncat(msg, other, L2C_MESSAGE_SIZE);
>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/edac/thunderx_edac.c: In function 'thunderx_ocx_lnk_threaded_isr':
> drivers/edac/thunderx_edac.c:1220:17: error: 'strncat' specified bound 1024 equals destination size [-Werror=stringop-overflow=]
>   1220 |                 strncat(msg, other, OCX_MESSAGE_SIZE);
>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Apparently the author of this driver expected strncat() to behave the
> way that strlcat() does, which uses the size of the destination buffer
> as its third argument rather than the length of the source buffer.
> The result is that there is no check on the size of the allocated
> buffer.
>
> Change it to use strncat().

s/strncat/strlcat

with that:

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Thanks!
--
Gustavo

> Fixes: 41003396f932 ("EDAC, thunderx: Add Cavium ThunderX EDAC driver")
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>   drivers/edac/thunderx_edac.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/edac/thunderx_edac.c b/drivers/edac/thunderx_edac.c
> index b9c5772da959..90d46e5c4ff0 100644
> --- a/drivers/edac/thunderx_edac.c
> +++ b/drivers/edac/thunderx_edac.c
> @@ -1133,7 +1133,7 @@ static irqreturn_t thunderx_ocx_com_threaded_isr(int irq, void *irq_id)
>   		decode_register(other, OCX_OTHER_SIZE,
>   				ocx_com_errors, ctx->reg_com_int);
>   
> -		strncat(msg, other, OCX_MESSAGE_SIZE);
> +		strlcat(msg, other, OCX_MESSAGE_SIZE);
>   
>   		for (lane = 0; lane < OCX_RX_LANES; lane++)
>   			if (ctx->reg_com_int & BIT(lane)) {
> @@ -1142,12 +1142,12 @@ static irqreturn_t thunderx_ocx_com_threaded_isr(int irq, void *irq_id)
>   					 lane, ctx->reg_lane_int[lane],
>   					 lane, ctx->reg_lane_stat11[lane]);
>   
> -				strncat(msg, other, OCX_MESSAGE_SIZE);
> +				strlcat(msg, other, OCX_MESSAGE_SIZE);
>   
>   				decode_register(other, OCX_OTHER_SIZE,
>   						ocx_lane_errors,
>   						ctx->reg_lane_int[lane]);
> -				strncat(msg, other, OCX_MESSAGE_SIZE);
> +				strlcat(msg, other, OCX_MESSAGE_SIZE);
>   			}
>   
>   		if (ctx->reg_com_int & OCX_COM_INT_CE)
> @@ -1217,7 +1217,7 @@ static irqreturn_t thunderx_ocx_lnk_threaded_isr(int irq, void *irq_id)
>   		decode_register(other, OCX_OTHER_SIZE,
>   				ocx_com_link_errors, ctx->reg_com_link_int);
>   
> -		strncat(msg, other, OCX_MESSAGE_SIZE);
> +		strlcat(msg, other, OCX_MESSAGE_SIZE);
>   
>   		if (ctx->reg_com_link_int & OCX_COM_LINK_INT_UE)
>   			edac_device_handle_ue(ocx->edac_dev, 0, 0, msg);
> @@ -1896,7 +1896,7 @@ static irqreturn_t thunderx_l2c_threaded_isr(int irq, void *irq_id)
>   
>   		decode_register(other, L2C_OTHER_SIZE, l2_errors, ctx->reg_int);
>   
> -		strncat(msg, other, L2C_MESSAGE_SIZE);
> +		strlcat(msg, other, L2C_MESSAGE_SIZE);
>   
>   		if (ctx->reg_int & mask_ue)
>   			edac_device_handle_ue(l2c->edac_dev, 0, 0, msg);