Re: [PATCH v3] kobject_uevent: Fix OOB access within zap_modalias_env()

[Lk Sii]

On 2024/5/30 21:14, Zijun Hu wrote:
> zap_modalias_env() wrongly calculates size of memory block to move, so
> will cause OOB memory access issue if variable MODALIAS is not the last
> one within its @env parameter, fixed by correcting size to memmove.
> 
> Fixes: 9b3fa47d4a76 ("kobject: fix suppressing modalias in uevents delivered over netlink")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
> ---
> V3: Correct inline comments and take Dmitry's suggestion
> V2: Correct commit messages and add inline comments
> 
> Previous discussion links:
> https://lore.kernel.org/lkml/ZlYo20ztfLWPyy5d@xxxxxxxxxx/
> https://lore.kernel.org/lkml/0b916393-eb39-4467-9c99-ac1bc9746512@xxxxxxxxxxx/T/#m8d80165294640dbac72f5c48d14b7ca4f097b5c7
> 
>  lib/kobject_uevent.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index 03b427e2707e..b7f2fa08d9c8 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -433,8 +433,23 @@ static void zap_modalias_env(struct kobj_uevent_env *env)
>  		len = strlen(env->envp[i]) + 1;
>  
>  		if (i != env->envp_idx - 1) {
> +			/* @env->envp[] contains pointers to @env->buf[]
> +			 * with @env->buflen chars, and we are removing
> +			 * variable MODALIAS here pointed by @env->envp[i]
> +			 * with length @len as shown below:
> +			 *
> +			 * 0               @env->buf[]      @env->buflen
> +			 * ---------------------------------------------
> +			 * ^             ^              ^              ^
> +			 * |             |->   @len   <-| target block |
> +			 * @env->envp[0] @env->envp[i]  @env->envp[i + 1]
> +			 *
> +			 * so the "target block" indicated above is moved
> +			 * backward by @len, and its right size is
> +			 * @env->buflen - (@env->envp[i + 1] - @env->envp[0]).
> +			 */
>  			memmove(env->envp[i], env->envp[i + 1],
> -				env->buflen - len);
> +				env->buflen - (env->envp[i + 1] - env->envp[0]));
>  
>  			for (j = i; j < env->envp_idx - 1; j++)
>  				env->envp[j] = env->envp[j + 1] - len;

Reviewed-by: Lk Sii <lk_sii@xxxxxxx>