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Destroyed Sysdig notes (markdown)

Henri DF
2016-04-28 14:13:39 -07:00
parent dcb5be6512
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Sysdig-notes.md

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## Notes on sysdig
### Missing/undecoded syscalls
- `fchmodat` needs to be decoded (from a quick experimentation, this is the one used by e.g. `/bin/chmod` on a recent linux system).
### Outbound UDP traffic support
UDP can be sent either via `sendto` or via `send`
#### `connect`
The `nc` tool uses `connect`. The commands below validate that sysdig decodes UDP `connect()`s properly. Note that the 'enter' connect does not pass the filter (the state table is only updated on the syscall return?)
`echo -n “foo” | nc -4u -w1 10.0.2.15 1500`
```
$ sudo sysdig 'proc.name=nc and fd.l4proto=udp'
1617 00:09:09.388994739 0 nc (12310) < connect res=0 tuple=10.0.2.15:52575->10.0.2.15:1500
1618 00:09:09.388995574 0 nc (12310) > fcntl fd=3(<4u>10.0.2.15:52575->10.0.2.15:1500) cmd=5(F_SETFL)
1619 00:09:09.388995725 0 nc (12310) < fcntl res=0(<p>)
1624 00:09:09.389009055 0 nc (12310) > write fd=3(<4u>10.0.2.15:52575->10.0.2.15:1500) size=9
1625 00:09:09.389026498 0 nc (12310) < write res=9 data=...foo...
1628 00:09:09.389028747 0 nc (12310) > shutdown fd=3(<4u>10.0.2.15:52575->10.0.2.15:1500) how=1(SHUT_WR)
1629 00:09:09.389029898 0 nc (12310) < shutdown res=0
```
#### `sendto`
```
00:23 vagrant@vagrant-ubuntu-trusty-64:~
$ sudo sysdig 'syscall.type = sendto'
684 00:23:20.935487226 0 a.out (12527) > sendto fd=3(<4>) size=16 tuple=0.0.0.0:12345->0.0.0.0:12345
685 00:23:20.935518814 0 a.out (12527) < sendto res=16 data=..09.....9......
```
```
00:22 vagrant@vagrant-ubuntu-trusty-64:~
$ sudo sysdig 'fd.l4proto=udp'
1104 00:23:09.296146765 0 a.out (12524) < sendto res=16 data=..09............
```
```
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
main()
{
int sd;
struct sockaddr_in server;
char buf[512];
int rc;
server.sin_family = AF_INET;
server.sin_addr.s_addr = htonl(INADDR_ANY);
server.sin_port = htons(12345);
sd = socket (AF_INET,SOCK_DGRAM,0);
bind ( sd, (struct sockaddr *) &server, sizeof(server));
sendto(sd, &server, sizeof(server), 0, (struct sockaddr *)&server, sizeof(server));
}
```
### Writing to the filesystem
From some quick c experimentation:
- It is possible to create a file with `O_RDONLY | O_CREAT` but it is not possible to then write to it.
- It is possible to open a file with `O_RDONLY | O_APPEND` but it is not possible to write to it.
```
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
int main(int argc, char *argv[])
{
int fd;
if(2 != argc) {
printf("\n Usage : \n");
return 1;
}
errno = 0;
fd = open(argv[1],O_RDONLY | O_CREAT);
if(-1 == fd) {
printf("\n open() failed with error [%s]\n",strerror(errno));
return 1;
} else {
printf("\n open() Successful\n");
}
const char *hello = "Hello";
int ret = write(fd, hello, sizeof(hello));
if(-1 == ret) {
printf("\n write() failed with error [%s]\n",strerror(errno));
return 1;
} else {
printf("\n write() Successful\n");
}
return 0;
}
```