Re: [PATCH v2] Fix stack smashing when handling PR_GET_PDEATHSIG

[Laurent Vivier <laurent@vivier.eu>]

Le 07/05/2020 à 15:03, Stephen Long a écrit :
> The bug was triggered by the following code on aarch64-linux-user:
> 
> #include <signal.h>
> #include <sys/prctl.h>
> 
> int main(void)
> {
>   int PDeathSig = 0;
>   if (prctl(PR_GET_PDEATHSIG, &PDeathSig) == 0 && PDeathSig == SIGKILL)
>     prctl(PR_GET_PDEATHSIG, 0);
>   return (PDeathSig == SIGKILL);
> }
> 
> Signed-off-by: Stephen Long <steplong@quicinc.com>
> Signed-off-by: Ana Pazos <apazos@quicinc.com>
> ---
> 
> I fixed the incorrect subject line. PR_GETDEATHSIG should be PR_GET_PDEATHSIG.
> Is there a test folder where I can include the code that triggered the bug?

Perhaps Alex Bennée knows?

> Also, I thought "int" can be 2 bytes on some machines.

According to my K&R, 4th edition, it could be on 16bit systems, like
PDP-11, but we don't support them ;)

Reviewed-by: Laurent Vivier <laurent@vivier.eu>

> 
>  linux-user/syscall.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 05f03919ff..91f91147ba 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -10256,7 +10256,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>              int deathsig;
>              ret = get_errno(prctl(arg1, &deathsig, arg3, arg4, arg5));
>              if (!is_error(ret) && arg2
> -                && put_user_ual(deathsig, arg2)) {
> +                && put_user_s32(deathsig, arg2)) {
>                  return -TARGET_EFAULT;
>              }
>              return ret;
>