[PATCH v4] system.3: Document bug and workaround when the command name starts with a hypen

[Michael Kerrisk (man-pages)]

On 1/8/21 3:28 PM, Alejandro Colomar (man-pages) wrote:
> 
> 
> On 1/8/21 3:22 PM, Alejandro Colomar wrote:
>> man-pages bug: 211029
>>  https://bugzilla.kernel.org/show_bug.cgi?id=211029
>>
>> Complete workaround
> 
> Maybe a bit more readable:
> Complete workaround example

Changed.

Thanks,

Michael

> 
> 
>> (it was too long for the page, but it may be useful here):
>>
>> ......
>>
>> $ sudo ln -s -T /usr/bin/echo /usr/bin/-echo;
>> $ cc -o system_hyphen -x c - ;
>> #include <stdlib.h>
>>
>> int
>> main(void)
>> {
>>     system(" -echo Hello world!");
>>     exit(EXIT_SUCCESS);
>> }
>>
>> $ ./system_hyphen;
>> Hello world!
>>
>> Reported-by: Ciprian Dorin Craciun <ciprian.craciun@gmail.com>
>> Cc: Florian Weimer <fweimer@redhat.com>
>> Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
>> ---
>>
>> D'oh!
>>
>>  man3/system.3 | 20 ++++++++++++++++++++
>>  1 file changed, 20 insertions(+)
>>
>> diff --git a/man3/system.3 b/man3/system.3
>> index 753d46f7d..ead35ab30 100644
>> --- a/man3/system.3
>> +++ b/man3/system.3
>> @@ -255,6 +255,26 @@ are not executed.
>>  Such risks are especially grave when using
>>  .BR system ()
>>  from a privileged program.
>> +.SH BUGS
>> +.\" [BUG 211029](https://bugzilla.kernel.org/show_bug.cgi?id=211029)
>> +.\" [Glibc bug](https://sourceware.org/bugzilla/show_bug.cgi?id=27143)
>> +.\" [POSIX bug](https://www.austingroupbugs.net/view.php?id=1440)
>> +If the command name starts with a hyphen,
>> +.BR sh (1)
>> +interprets the command name as an option,
>> +and the behavior is undefined.
>> +(See the
>> +.B \-c
>> +option to
>> +.BR sh (1).)
>> +To work around this problem,
>> +prepend the command with a space as in the following call:
>> +.PP
>> +.RS 4
>> +.EX
>> +    system(" \-unfortunate\-command\-name");
>> +.EE
>> +.RE
>>  .SH SEE ALSO
>>  .BR sh (1),
>>  .BR execve (2),
>>
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/