Sandbox: Caught a bad syscall attempt (syscall poll)
```
(Sandbox) Caught a bad syscall attempt (syscall poll)
/usr/bin/tor(+0x1a5baa)[0x560fee34ebaa]
/lib/x86_64-linux-gnu/libc.so.6(__poll+0x10)[0x7fd66246c690]
/lib/x86_64-linux-gnu/libc.so.6(__poll+0x10)[0x7fd66246c690]
/lib/x86_64-linux-gnu/libc.so.6(+0x11b573)[0x7fd6624a8573]
/lib/x86_64-linux-gnu/libc.so.6(+0x11c189)[0x7fd6624a9189]
/lib/x86_64-linux-gnu/libc.so.6(+0x1187f2)[0x7fd6624a57f2]
/lib/x86_64-linux-gnu/libc.so.6(+0x118a3e)[0x7fd6624a5a3e]
/lib/x86_64-linux-gnu/libc.so.6(getpwnam_r+0x1cd)[0x7fd6624443ed]
/lib/x86_64-linux-gnu/libc.so.6(getpwnam+0x90)[0x7fd662443d20]
/usr/bin/tor(tor_getpwnam+0x29)[0x560fee3369e9]
/usr/bin/tor(check_private_dir+0x9f)[0x560fee3480bf]
/usr/bin/tor(create_keys_directory+0x34)[0x560fee29b924]
/usr/bin/tor(init_keys+0x89)[0x560fee2439d9]
/usr/bin/tor(do_main_loop+0x54)[0x560fee1fd5b4]
/usr/bin/tor(tor_run_main+0x275)[0x560fee1fef25]
/usr/bin/tor(tor_main+0x3a)[0x560fee1f836a]
/usr/bin/tor(main+0x19)[0x560fee1f80d9]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7fd6623ad2b1]
/usr/bin/tor(_start+0x2a)[0x560fee1f812a]
```
config
```
OfflineMasterKey 1
RunAsDaemon 0
Log notice syslog
OutboundBindAddress xxxxxx
SocksPort 0
User xxxx
DataDirectory xxxxx
ORPort xxxxxxx
ORPort xxxxxxxxx
OutboundBindAddress xxxxxxx
DirPort xxxxxxxxx
ControlSocket 0
CookieAuthentication 0
Sandbox 1
ExitRelay 0
ExitPolicy reject *:*
```
os: debian 9 on KVM
reproducible with:
0.3.2.9-1~d90.stretch+1
0.3.3.2-alpha-1~d90.stretch+1
0.3.4.0-alpha-dev-20180220T150525Z-1~d90.stretch+1
issue