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Date: Thu, 14 Mar 2019 07:44:55 -0500
From: "A. Wilcox" <awilfox@...lielinux.org>
To: musl@...ts.openwall.com
Cc: Natanael ncopa Copa <ncopa@...inelinux.org>
Subject: Re: segfault on sscanf
On Mar 14, 2019, at 4:46 AM, Marian Buschsieweke <marian.buschsieweke@...u.de> wrote:
>
> Hi,
>
> running pdflatex on Alpine Linux for a specific document resulted in a
> segfault, which I could trace down to a specific call to sscanf. This is a
> minimum example to reproduce that segfault:
>
> #include <stdio.h>
>
> int main(void) {
> const char *too_parse = "0 1 -1 0";
> double f1,f2,f3,f4;
> char dummy;
> sscanf(too_parse, " %lf %lf %lf %lf %c", &f1, &f2, &f3, &f4, &dummy);
>
> printf("f1=%f, f2=%f, f3=%f, f4=%f, dummy=\"%c\"\n", f1, f2, f3, f4, dummy);
>
> return 0;
> }
>
> This is the backtrace:
>
> #0 0x00007ffff7fb7eba in vfscanf (f=f@...ry=0x7fffffffe6f8,
> fmt=<optimized out>, ap=ap@...ry=0x7fffffffe7f8) at src/stdio/vfscanf.c:262
> #1 0x00007ffff7fb971a in vsscanf (s=<optimized out>, fmt=<optimized out>,
> ap=ap@...ry=0x7fffffffe7f8) at src/stdio/vsscanf.c:14
> #2 0x00007ffff7fb594d in sscanf (s=<optimized out>, fmt=<optimized out>)
> at src/stdio/sscanf.c:9
> #3 0x0000555555555213 in main () at test.c:7
>
> I have the package Alpine Linux package musl-1.1.21-r0 installed, which is musl
> version 1.1.21 with minimal changes.
>
> Kind regards,
> Marian
Hi Marian,
In your example you have four fields, but sscanf is looking for five. You have run off the end of the string. This is illegal/UB. Is this intentional in your test case?
Best,
—arw
--
A. Wilcox (Sent from my iPhone - not signed)
Project Lead, Adélie Linux
https://adelielinux.org
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