Rainer Weikusat <[email protected]> writes:
> Ben Hutchings <[email protected]> writes:
[...]
>> unix: Fix potential double-unlock in unix_dgram_sendmsg()
>>
>> A datagram socket may be peered with itself, so that sk == other. We
>> use unix_state_double_lock() to lock sk and other in the right order,
>> which also guards against this and only locks the socket once, but we
>> then end up trying to unlock it twice. Add the check for sk != other.
[...]
> other was found via
>
> if (!other) {
> err = -ECONNRESET;
> if (sunaddr == NULL)
> goto out_free;
>
> other = unix_find_other(net, sunaddr, namelen, sk->sk_type,
> hash, &err);
> if (other == NULL)
> goto out_free;
> }
>
> and the if-block leading to the double lock should never have been
> executed as it's supposed to deal with the case where sk is connect to
> other but other not to sk (eg, /dev/log).
Test program triggering a double unlock (w/o the MSG_DONTWAIT, it blocks
which it isn't supposed to do):
--------
#include <stdio.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
#define SUN_NAME "\0other-is-me"
int main(int argc, char **argv)
{
struct sockaddr_un sun;
unsigned max;
int sk, rc;
sk = socket(AF_UNIX, SOCK_DGRAM, 0);
sun.sun_family = AF_UNIX;
strncpy(sun.sun_path, SUN_NAME, sizeof(sun.sun_path));
bind(sk, (struct sockaddr *)&sun, sizeof(sun));
max = 12;
do
sendto(sk, &sun, sizeof(sun), MSG_DONTWAIT,
(struct sockaddr *)&sun, sizeof(sun));
while (--max);
return 0;
}
