diff options
| author | Daniel Borkmann <daniel@iogearbox.net> | 2021-08-09 12:43:17 +0200 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-08-10 10:10:10 +0200 |
| commit | 51e1bb9eeaf7868db56e58f47848e364ab4c4129 (patch) | |
| tree | fcc65c981be80c0ff7393bcc1dea857909416450 /include/linux | |
| parent | 71330842ff93ae67a066c1fa68d75672527312fa (diff) | |
bpf: Add lockdown check for probe_write_user helper
Back then, commit 96ae52279594 ("bpf: Add bpf_probe_write_user BPF helper
to be called in tracers") added the bpf_probe_write_user() helper in order
to allow to override user space memory. Its original goal was to have a
facility to "debug, divert, and manipulate execution of semi-cooperative
processes" under CAP_SYS_ADMIN. Write to kernel was explicitly disallowed
since it would otherwise tamper with its integrity.
One use case was shown in cf9b1199de27 ("samples/bpf: Add test/example of
using bpf_probe_write_user bpf helper") where the program DNATs traffic
at the time of connect(2) syscall, meaning, it rewrites the arguments to
a syscall while they're still in userspace, and before the syscall has a
chance to copy the argument into kernel space. These days we have better
mechanisms in BPF for achieving the same (e.g. for load-balancers), but
without having to write to userspace memory.
Of course the bpf_probe_write_user() helper can also be used to abuse
many other things for both good or bad purpose. Outside of BPF, there is
a similar mechanism for ptrace(2) such as PTRACE_PEEK{TEXT,DATA} and
PTRACE_POKE{TEXT,DATA}, but would likely require some more effort.
Commit 96ae52279594 explicitly dedicated the helper for experimentation
purpose only. Thus, move the helper's availability behind a newly added
LOCKDOWN_BPF_WRITE_USER lockdown knob so that the helper is disabled under
the "integrity" mode. More fine-grained control can be implemented also
from LSM side with this change.
Fixes: 96ae52279594 ("bpf: Add bpf_probe_write_user BPF helper to be called in tracers")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/security.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/security.h b/include/linux/security.h index 724d7a4a0c91..5b7288521300 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -120,6 +120,7 @@ enum lockdown_reason { LOCKDOWN_MMIOTRACE, LOCKDOWN_DEBUGFS, LOCKDOWN_XMON_WR, + LOCKDOWN_BPF_WRITE_USER, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_KCORE, LOCKDOWN_KPROBES, |