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Message-ID: <1587641710830.20636@trust-in-soft.com>
Date: Thu, 23 Apr 2020 11:34:26 +0000
From: Pascal Cuoq <cuoq@...st-in-soft.com>
To: "musl@...ts.openwall.com" <musl@...ts.openwall.com>
Subject: Re: Invalid pointer subtractions in __shlim and __shgetc
Hello again,
Rich Felker <dalias@...c.org> wrote:
> I think this patch may result in wrong error behavior on a trivial
> scanf that doesn't try to read anything. Instead it should be:
>
> if (!f->rpos) __toread(f);
> if (!f->rpos) goto input_fail;
>
> so that the error path is taken only on failure to enter read mode,
> not on EOF.
This has indeed fixed the invalid comparisons that were observed
from the tests I mentioned earlier, but a different test still has
the same problem.
As of commit 33338eb, the function wcstox does:
f.rpos = f.rend = 0;
f.buf = buf + 4;
(https://git.musl-libc.org/cgit/musl/tree/src/stdlib/wcstol.c?id=33338ebc853d37c80f0f236cc7a92cb0acc6aace#n38 )
It then passes the address of this f to shlim (line 45), causing the same invalid pointer subtraction f->buf - f->rpos that has already been discussed in this thread.
Best regards,
Pascal
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