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Date: Tue, 12 Feb 2019 14:55:19 +0000
From: Ponnuvel Palaniyappan <pponnuvel@...il.com>
To: musl@...ts.openwall.com
Subject: Re: Bug in gets function?
> Is gets(s) equivalent to scanf("%[^\n]%*1[\n]",s)?
I think it has at least one minor issue: it doesn't null-terminate the
buffer on empty input i.e., just a newline as input.
Regards,
Ponnuvel
On Tue, Feb 12, 2019 at 2:42 PM James Larrowe <larrowe.semaj11@...il.com>
wrote:
> I could probably try patching it. That C99 specification seems descriptive
> enough.
>
> On Mon, Feb 11, 2019 at 10:51 PM Rich Felker <dalias@...c.org> wrote:
>
>> 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
>>
>
--
Regards,
Ponnuvel P
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