RET_KILL_THREAD doesn't work well for Go because it will
kill only the offending thread and leave the process hanging.
RET_TRAP can be masked out and it's not guaranteed to kill
the process. RET_KILL_PROCESS is available since 4.14.
For older kernel, continue to use RET_TRAP as this is the
best option (likely to kill process, easy to debug).
PiperOrigin-RevId: 222357867
Change-Id: Icc1d7d731274b16c2125b7a1ba4f7883fbdb2cbd
Pseudoterminal job control signals are meant to be received and handled by the
sandbox process, but if the ptrace stubs are running in the same process group,
they will receive the signals as well and inject then into the sentry kernel.
This can result in duplicate signals being delivered (often to the wrong
process), or a sentry panic if the ptrace stub is inactive.
This CL makes the ptrace stub run in a new session.
PiperOrigin-RevId: 218536851
Change-Id: Ie593c5687439bbfbf690ada3b2197ea71ed60a0e
This is a defense-in-depth measure. If the sentry is compromised, this prevents
system call injection to the stubs. There is some complexity with respect to
ptrace and seccomp interactions, so this protection is not really available
for kernel versions < 4.8; this is detected dynamically.
Note that this also solves the vsyscall emulation issue by adding in
appropriate trapping for those system calls. It does mean that a compromised
sentry could theoretically inject these into the stub (ignoring the trap and
resume, thereby allowing execution), but they are harmless.
PiperOrigin-RevId: 216647581
Change-Id: Id06c232cbac1f9489b1803ec97f83097fcba8eb8
If the child stubs are killed by any unmaskable signal (e.g. SIGKILL), then
the parent process will similarly be killed, resulting in the death of all
other stubs.
The effect of this is that if the OOM killer selects and kills a stub, the
effect is the same as though the OOM killer selected and killed the sentry.
PiperOrigin-RevId: 202219984
Change-Id: I0b638ce7e59e0a0f4d5cde12a7d05242673049d7
Fabricio Voznika
Adin Scannell
Nicolas Lacasse
Ian Gudger
Googler