On Tue, May 28, 2024 at 11:19:07AM +0800, 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>
> ---
> V1 -> V2: Correct commit messages and add inline comments
>
> V1 discussion link:
> 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..f22366be020c 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 elements, and we want to
> + * remove variable MODALIAS pointed by
> + * @env->envp[i] with length @len as shown below:
> + *
> + * 0 @env->buf[] @env->buflen
> + * ----------------------------------------
> + * ^ ^ ^
> + * |-> @len <-| target block |
> + * @env->envp[i] @env->envp[i+1]
> + *
> + * so the "target block" indicated above is moved
> + * backward by @len, and its right size is
> + * (@env->buf + @env->buflen - @env->envp[i + 1]).
> + */
> memmove(env->envp[i], env->envp[i + 1],
> - env->buflen - len);
> + env->buf + env->buflen - env->envp[i + 1]);
Thank you for noticing this, it is indeed a bug.
I wonder if this would not be expressed better as:
tail_len = env->buflen - (env->envp[i + 1] - env->envp[0]);
memmove(env->envp[i], env->envp[i + 1], tail_len);
and we would not need the large comment.
Otherwise:
Acked-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
>
> for (j = i; j < env->envp_idx - 1; j++)
> env->envp[j] = env->envp[j + 1] - len;
> --
> 2.7.4
>
Thanks.
--
Dmitry
