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Date: Mon, 11 Feb 2019 22:51:06 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: Bug in gets function?
On Mon, Feb 11, 2019 at 10:48:38PM -0500, Rich Felker wrote:
> On Mon, Feb 11, 2019 at 06:55:24PM -0800, Keyhan Vakil wrote:
> > Hi. It seems that the gets function does not follow the C99 spec. In
> > particular, if the input contains a null byte in the middle of the
> > input, then the new-line character is not discarded.
> >
> > For reference, here's the relevant part in the C99 standard
> > (7.19.7.7):
> >
> > > The gets function reads characters from the input stream pointed to
> > > by stdin, into the array pointed to by s, until end-of-file is
> > > encountered or a new-line character is read. Any new-line character
> > > is discarded, and a null character is written immediately after the
> > > last character read into the array.
> >
> > Here is an example:
> >
> > #include <stdio.h>
> > char s[8];
> > int main() {
> > gets(s);
> > for (int i = 0; i < sizeof s; i++) {
> > printf("%02x ", s[i]);
> > }
> > printf("\n");
> > return 0;
> > }
> >
> > When compiled against gcc:
> >
> > $ echo -e 'A\x00B' | ./a.out
> > 41 00 42 00 00 00 00 00
> >
> > When compiled against musl:
> >
> > $ echo -e 'A\x00B' | ./a.out
> > 41 00 42 0a 00 00 00 00
> >
> > Note the terminating newline, which contradicts the spec.
>
> I think this bug report is correct; however the gets function is
> awful, removed in C11, and should never be used. :-)
>
> I will see what can be done to fix it though.
Is gets(s) equivalent to scanf("%[^\n]%*1[\n]",s)? If so that would be
an appropriately hideous way to implement it that avoids the current
bug? :-)
Rich
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