bug report: select on unconnected sockets

bug report: select on unconnected sockets

[Radu Greab]

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Sorry if this is already known: on a RH 7.0 system with kernel 2.4.2
or 2.4.3, a select on an unconnected socket incorrectly says that the
socket is ready for input and output. Of course, reading from the socket
file descriptor returns -1 and errno is set to ENOTCONN as shown in
the strace output:

socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
select(4, [3], [3], [3], {0, 0})        = 2 (in [3], out [3], left {0, 0})
read(3, 0xbffff668, 1024)               = -1 ENOTCONN (Transport endpoint is not connected)

I attached a small example program to reproduce the bug.


Thanks,
Radu Greab

PS: please CC me your eventual replies as I'm not subscribed to the
list.



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#include <stdio.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>

int main(int argc, char **argv) {
  fd_set rfds, wfds, efds;
  int s, rc;
  struct timeval timeout;
  char buf[1025];

  s = socket(PF_INET, SOCK_STREAM, 0);
  if (s == -1) {
    perror("couldn't create socket");
    return -1;
  }

  FD_ZERO(&rfds);
  FD_SET(s, &rfds);
  FD_ZERO(&wfds);
  FD_SET(s, &wfds);
  FD_ZERO(&efds);
  FD_SET(s, &efds);
  timeout.tv_sec = timeout.tv_usec = 0;
  rc = select(s + 1, &rfds, &wfds, &efds, &timeout);
  if (rc == -1) {
    perror("select");
    return -1;
  }
  printf("select result=%d\n", rc);
  if (FD_ISSET(s, &rfds)) {
    rc = read(s, buf, 1024);
    if (rc == -1) {
      perror("read");
      return -1;
    }
    printf("read result=%d\n", rc);
  }

  return 0;
}

Re: bug report: select on unconnected sockets

[john slee]

On Sat, Mar 31, 2001 at 06:44:20PM +0300, Radu Greab wrote:
> Sorry if this is already known: on a RH 7.0 system with kernel 2.4.2
> or 2.4.3, a select on an unconnected socket incorrectly says that the
> socket is ready for input and output. Of course, reading from the socket
> file descriptor returns -1 and errno is set to ENOTCONN as shown in
> the strace output:
> 
> socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
> select(4, [3], [3], [3], {0, 0})        = 2 (in [3], out [3], left {0, 0})
> read(3, 0xbffff668, 1024)               = -1 ENOTCONN (Transport endpoint is not connected)
> 
> I attached a small example program to reproduce the bug.

bleah.  which one is supposed to be right?

linux 2.4
---------
$ uname -a
Linux XXXXX 2.4.2-ac20 #8 Wed Mar 14 01:53:05 EST 2001 i686 unknown
$ ./t
select result=2
read: Transport endpoint is not connected

linux 2.2
---------
$ uname -a
Linux XXXXX 2.2.18 #1 Thu Dec 21 21:13:10 EST 2000 i586 unknown
$ ./t
select result=1

solaris
-------
$ uname -a
SunOS XXXXX 5.7 Generic_106541-07 sun4m sparc sun4m
$ ./t
select result=0

-- 
"Bobby, jiggle Grandpa's rat so it looks alive, please" -- gary larson

Re: bug report: select on unconnected sockets

[Radu Greab]

On Sun, 1 Apr 2001 02:15 +1000, john slee wrote:
 > On Sat, Mar 31, 2001 at 06:44:20PM +0300, Radu Greab wrote:
 > > Sorry if this is already known: on a RH 7.0 system with kernel 2.4.2
 > > or 2.4.3, a select on an unconnected socket incorrectly says that the
 > > socket is ready for input and output. Of course, reading from the socket
 > > file descriptor returns -1 and errno is set to ENOTCONN as shown in
 > > the strace output:
 > > 
 > > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
 > > select(4, [3], [3], [3], {0, 0})        = 2 (in [3], out [3], left {0, 0})
 > > read(3, 0xbffff668, 1024)               = -1 ENOTCONN (Transport endpoint is not connected)
 > > 
 > > I attached a small example program to reproduce the bug.
 > 
 > bleah.  which one is supposed to be right?

I think that the Solaris one is right.

 > 
 > linux 2.4
 > ---------
 > $ uname -a
 > Linux XXXXX 2.4.2-ac20 #8 Wed Mar 14 01:53:05 EST 2001 i686 unknown
 > $ ./t
 > select result=2
 > read: Transport endpoint is not connected

Select says that the socket is ready for both input and output. A read
results in ENOTCONN, a write results in EPIPE.

 > linux 2.2
 > ---------
 > $ uname -a
 > Linux XXXXX 2.2.18 #1 Thu Dec 21 21:13:10 EST 2000 i586 unknown
 > $ ./t
 > select result=1

Select says that the socket is ready for output, but a write results
in EPIPE.

 > 
 > solaris
 > -------
 > $ uname -a
 > SunOS XXXXX 5.7 Generic_106541-07 sun4m sparc sun4m
 > $ ./t
 > select result=0

And Digital Unix is right too:

$ uname -a
OSF1 XXX V4.0 1229 alpha
$ ./a.out
select result=0


Thanks,
Radu Greab