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Re: [Qemu-trivial] [PATCH] cutils: Assert in-range base for string-to-in


From: Laurent Vivier
Subject: Re: [Qemu-trivial] [PATCH] cutils: Assert in-range base for string-to-integer conversions
Date: Thu, 6 Dec 2018 17:40:17 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1

Le 06/12/2018 à 16:18, Eric Blake a écrit :
> POSIX states that the value of endptr is unspecified if strtol()
> fails with EINVAL due to an invalid base argument.  Since none of
> the callers to check_strtox_error() initialized endptr, we could
> end up propagating uninitialized data back to a caller on error.
> However, passing an out-of-range base is already a sign of poor
> programming, so let's just assert that base is in range, at which
> point check_strtox_error() can be tightened to assert that it is
> receiving an initialized ep that points somewhere within the
> caller's original string, regardless of whether strto*() succeeded
> or failed with ERANGE.
> 
> Reported-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Signed-off-by: Eric Blake <address@hidden>
> ---
> 
> Also tested that this does not negatively impact David's pending
> additions of qemu_strtod{,_finite}().  Thus:
> Based-on: <address@hidden>
> 
>  util/cutils.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/util/cutils.c b/util/cutils.c
> index 91930d1bbeb..e098debdc0c 100644
> --- a/util/cutils.c
> +++ b/util/cutils.c
> @@ -278,6 +278,7 @@ int qemu_strtosz_metric(const char *nptr, const char 
> **end, uint64_t *result)
>  static int check_strtox_error(const char *nptr, char *ep,
>                                const char **endptr, int libc_errno)
>  {
> +    assert(ep >= nptr);
>      if (endptr) {
>          *endptr = ep;
>      }
> @@ -325,6 +326,7 @@ int qemu_strtoi(const char *nptr, const char **endptr, 
> int base,
>      char *ep;
>      long long lresult;
> 
> +    assert((unsigned) base <= 36 && base != 1);

If you want to play with type, I think you can do:

   assert((unsigned)(base - 2) <= 34)

Thanks,
Laurent



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