Description Pierre Ossman 2013-11-13 10:29:46 CET

We introduced a control socket in rdesktop in order to do session sharing. Igge managed to get rdesktop into a tight loop, eating 100% CPU, and the socket is involved:


 8253 johig     20   0  557m 7032 1656 R 100.3  0.1  51:17.83 rdesktop                                                                                                                                             

[root@castro ~]# strace -p 8253
Process 8253 attached - interrupt to quit
recvfrom(6, "", 1024, 0, NULL, NULL)    = 0
recvfrom(9, "", 1024, 0, NULL, NULL)    = 0
recvfrom(4, 0x2799cc4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
select(10, [3 4 5 6 9], [], NULL, {0, 200000}) = 2 (in [6 9], left {0, 199997})
recvfrom(6, "", 1024, 0, NULL, NULL)    = 0
recvfrom(9, "", 1024, 0, NULL, NULL)    = 0
recvfrom(4, 0x2799cc4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
select(10, [3 4 5 6 9], [], NULL, {0, 200000}) = 2 (in [6 9], left {0, 199996})
recvfrom(6, "", 1024, 0, NULL, NULL)    = 0
recvfrom(9, "", 1024, 0, NULL, NULL)    = 0
recvfrom(4, 0x2799cc4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
select(10, [3 4 5 6 9], [], NULL, {0, 200000}) = 2 (in [6 9], left {0, 199996})
recvfrom(6, "", 1024, 0, NULL, NULL)    = 0
recvfrom(9, "", 1024, 0, NULL, NULL)    = 0
recvfrom(4, 0x2799cc4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
select(10, [3 4 5 6 9], [], NULL, {0, 200000}) = 2 (in [6 9], left {0, 199996})
recvfrom(6, "", 1024, 0, NULL, NULL)    = 0
recvfrom(9, "", 1024, 0, NULL, NULL)    = 0
recvfrom(4, 0x2799cc4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
select(10, [3 4 5 6 9], [], NULL, {0, 200000}) = 2 (in [6 9], left {0, 199996})
recvfrom(6, "", 1024, 0, NULL, NULL)    = 0
recvfrom(9, "", 1024, 0, NULL, NULL)    = 0
recvfrom(4, 0x2799cc4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
select(10, [3 4 5 6 9], [], NULL, {0, 200000}) = 2 (in [6 9], left {0, 199996})
recvfrom(6, "", 1024, 0, NULL, NULL)    = 0
recvfrom(9, "", 1024, 0, NULL, NULL)    = 0
recvfrom(4, 0x2799cc4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
^CProcess 8253 detached
[root@castro ~]# ll /proc/8253/fd
total 0
lr-x------. 1 johig johig 64 Nov 13 10:23 0 -> pipe:[2784234325]
l-wx------. 1 johig johig 64 Nov 13 10:23 1 -> /var/opt/thinlinc/sessions/johig/1/xinit.log
l-wx------. 1 johig johig 64 Nov 13 10:23 2 -> pipe:[2784234326]
lrwx------. 1 johig johig 64 Nov 13 10:23 3 -> socket:[2784234332]
lrwx------. 1 johig johig 64 Nov 13 10:23 4 -> socket:[2784234333]
lrwx------. 1 johig johig 64 Nov 13 10:23 5 -> socket:[2616342855]
lrwx------. 1 johig johig 64 Nov 13 10:22 6 -> socket:[2616342202]
lr-x------. 1 johig johig 64 Nov 13 10:23 7 -> pipe:[2784234295]
l-wx------. 1 johig johig 64 Nov 13 10:23 8 -> pipe:[2784234295]
lrwx------. 1 johig johig 64 Nov 13 10:22 9 -> socket:[2616342223]
[root@castro ~]# ll /proc/8253/fd^C
[root@castro ~]# netstat -ne |grep 2616342202
unix  2      [ ]         STREAM     CONNECTED     2616342202 /home/johig/.local/share/rdesktop/ctrl/2e1aeb3a90302808c9e0bd303f20140c86d976f6.ctl
[root@castro ~]# netstat -ne |grep 2616342223
unix  2      [ ]         STREAM     CONNECTED     2616342223 /home/johig/.local/share/rdesktop/ctrl/2e1aeb3a90302808c9e0bd303f20140c86d976f6.ctl


Since recvfrom() returns 0, I guess the socket is simply closed and we do not handle this common case?