TestPatchHugeSeccompFilterDoesNotBlock is only testing the
disassembleFilter function. There is no need to invoke PatchAndLoad
which has the side effect of loading a seccomp profile.
Co-authored-by: Danail Branekov <danailster@gmail.com>
Co-authored-by: Kieron Browne <kbrowne@vmware.com>
Signed-off-by: Kieron Browne <kbrowne@vmware.com>
Signed-off-by: Danail Branekov <danailster@gmail.com>
There is a potential deadlock where the ExportBPF method call writes to
a pipe but the pipe is not read until after the method call returns.
ExportBPF might fill the pipe buffer, in which case it will block
waiting for a read on the other side which can't happen until the method
returns.
Here we concurrently read from the pipe into a buffer to ensure
ExportBPF will always return.
Co-authored-by: Kieron Browne <kbrowne@vmware.com>
Co-authored-by: Danail Branekov <danailster@gmail.com>
Signed-off-by: Kieron Browne <kbrowne@vmware.com>
Signed-off-by: Danail Branekov <danailster@gmail.com>
This test fails to compile on i386:
> libcontainer/seccomp/patchbpf/enosys_linux_test.go:180:20: constant 3735928559 overflows int
> libcontainer/seccomp/patchbpf/enosys_linux_test.go:204:19: constant 3735928559 overflows int
> libcontainer/seccomp/patchbpf/enosys_linux_test.go:227:25: constant 3735928559 overflows int
This is because golang.org/x/net/bpf returns an int from their emulated
BPF VM implementation when they should really be returning uint32.
Fix by switching to uint32 in the test code.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
The correct way to do that conversion according to
https://pkg.go.dev/syscall#Errno is:
```
err = nil
if errno != 0 {
err = errno
}
```
In this case the error check will always report a false positive in
unix.RawSyscall(unix.SYS_SECCOMP, ...), probably nobody has faced this
problem because the code takes the other path in most of the cases.
Fixes: 7a8d7162f9 ("seccomp: prepend -ENOSYS stub to all filters")
Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
This function is called by `InitSeccomp`, but only when compiled
with seccomp (and cgo) enabled, so should not be needed for other
situations.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Having -EPERM is the default was a fairly significant mistake from a
future-proofing standpoint in that it makes any new syscall return a
non-ignorable error (from glibc's point of view). We need to correct
this now because faccessat2(2) is something glibc critically needs to
have support for, but they're blocked on container runtimes because we
return -EPERM unconditionally (leading to confusion in glibc). This is
also a problem we're probably going to keep running into in the future.
Unfortunately there are several issues which stop us from having a clean
solution to this problem:
1. libseccomp has several limitations which require us to emulate
behaviour we want:
a. We cannot do logic based on syscall number, meaning we cannot
specify a "largest known syscall number";
b. libseccomp doesn't know in which kernel version a syscall was
added, and has no API for "minimum kernel version" so we cannot
simply ask libseccomp to generate sane -ENOSYS rules for us.
c. Additional seccomp rules for the same syscall are not treated as
distinct rules -- if rules overlap, seccomp will merge them. This
means we cannot add per-syscall -EPERM fallbacks;
d. There is no inverse operation for SCMP_CMP_MASKED_EQ;
e. libseccomp does not allow you to specify multiple rules for a
single argument, making it impossible to invert OR rules for
arguments.
2. The runtime-spec does not have any way of specifying:
a. The errno for the default action;
b. The minimum kernel version or "newest syscall at time of profile
creation"; nor
c. Which syscalls were intentionally excluded from the allow list
(weird syscalls that are no longer used were excluded entirely,
but Docker et al expect those syscalls to get EPERM not ENOSYS).
3. Certain syscalls should not return -ENOSYS (especially only for
certain argument combinations) because this could also trigger glibc
confusion. This means we have to return -EPERM for certain syscalls
but not as a global default.
4. There is not an obvious (and reasonable) upper limit to syscall
numbers, so we cannot create a set of rules for each syscall above
the largest syscall number in libseccomp. This means we must handle
inverse rules as described below.
5. Any syscall can be specified multiple times, which can make
generation of hotfix rules much harder.
As a result, we have to work around all of these things by coming up
with a heuristic to stop the bleeding. In the future we could hopefully
improve the situation in the runtime-spec and libseccomp.
The solution applied here is to prepend a "stub" filter which returns
-ENOSYS if the requested syscall has a larger syscall number than any
syscall mentioned in the filter. The reason for this specific rule is
that syscall numbers are (roughly) allocated sequentially and thus newer
syscalls will (usually) have a larger syscall number -- thus causing our
filters to produce -ENOSYS if the filter was written before the syscall
existed.
Sadly this is not a perfect solution because syscalls can be added
out-of-order and the syscall table can contain holes for several
releases. Unfortuntely we do not have a nicer solution at the moment
because there is no library which provides information about which Linux
version a syscall was introduced in. Until that exists, this workaround
will have to be good enough.
The above behaviour only happens if the default action is a blocking
action (in other words it is not SCMP_ACT_LOG or SCMP_ACT_ALLOW). If the
default action is permissive then we don't do any patching.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Kieron Browne