On Fri, May 24, 2024 at 01:15:01PM +0800, quic_zijuhu wrote:
> On 5/24/2024 12:33 PM, Greg KH wrote:
> > On Fri, May 24, 2024 at 12:20:03PM +0800, Zijun Hu wrote:
> >> zap_modalias_env() wrongly calculates size of memory block
> >> to move, so maybe cause OOB memory access issue, fixed by
> >> correcting size to memmove.
> >
> > "maybe" or "does"? That's a big difference :)
> >
> i found this issue by reading code instead of really meeting this issue.
> this issue should be prone to happen if there are more than 1 other
> environment vars.
But does it? Given that we have loads of memory checkers, and I haven't
ever seen any report of any overrun, it would be nice to be sure.
> do you have suggestion about term to use?
Some confirmation that this really is the case would be nice :)
> >> Fixes: 9b3fa47d4a76 ("kobject: fix suppressing modalias in uevents delivered over netlink")
> >> Cc: stable@xxxxxxxxxxxxxxx
> >> Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
> >> ---
> >> lib/kobject_uevent.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> >> index 03b427e2707e..f153b4f9d4d9 100644
> >> --- a/lib/kobject_uevent.c
> >> +++ b/lib/kobject_uevent.c
> >> @@ -434,7 +434,7 @@ static void zap_modalias_env(struct kobj_uevent_env *env)
> >>
> >> if (i != env->envp_idx - 1) {
> >> memmove(env->envp[i], env->envp[i + 1],
> >> - env->buflen - len);
> >> + env->buf + env->buflen - env->envp[i + 1]);
> >
> > How is this "more correct"? Please explain it better, this logic is not
> > obvious at all.
> >
> env->envp[] contains pointers to env->buf[] with length env->buflen,
> we want to delete environment variable pointed by env->envp[i] with
> length @len as shown below.
>
> env->buf[] |-> target block <-|
> 0-----------------------------------------env->buflen
> ^ ^
> | -> @len <- |
> env->envp[i] env->envp[i+1]
>
> so move "target block" forward by @len, so size of target block is
> env->buf + env->buflen - env->envp[i+1] instead of env->buflen
> -len.
>
> do you suggest add inline comments to explain it ?
Yes please.
thanks,
greg k-h
