| Message ID | 20190715195946.223443-24-matthewgarrett@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Kernel lockdown functionality | expand |
On 7/15/19 9:59 PM, Matthew Garrett wrote: > From: David Howells <dhowells@redhat.com> > > bpf_read() and bpf_read_str() could potentially be abused to (eg) allow > private keys in kernel memory to be leaked. Disable them if the kernel > has been locked down in confidentiality mode. > > Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com> > Signed-off-by: Matthew Garrett <mjg59@google.com> > cc: netdev@vger.kernel.org > cc: Chun-Yi Lee <jlee@suse.com> > cc: Alexei Starovoitov <alexei.starovoitov@gmail.com> > Cc: Daniel Borkmann <daniel@iogearbox.net> > --- > include/linux/security.h | 1 + > kernel/trace/bpf_trace.c | 10 ++++++++++ > security/lockdown/lockdown.c | 1 + > 3 files changed, 12 insertions(+) > > diff --git a/include/linux/security.h b/include/linux/security.h > index 987d8427f091..8dd1741a52cd 100644 > --- a/include/linux/security.h > +++ b/include/linux/security.h > @@ -118,6 +118,7 @@ enum lockdown_reason { > LOCKDOWN_INTEGRITY_MAX, > LOCKDOWN_KCORE, > LOCKDOWN_KPROBES, > + LOCKDOWN_BPF_READ, > LOCKDOWN_CONFIDENTIALITY_MAX, > }; > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index ca1255d14576..605908da61c5 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -142,7 +142,12 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr) > { > int ret; > > + ret = security_locked_down(LOCKDOWN_BPF_READ); > + if (ret) > + goto out; > + > ret = probe_kernel_read(dst, unsafe_ptr, size); > +out: > if (unlikely(ret < 0)) > memset(dst, 0, size); Hmm, does security_locked_down() ever return a code > 0 or why do you have the double check on return code? If not, then for clarity the ret code from security_locked_down() should be checked as 'ret < 0' as well and out label should be at the memset directly instead. > @@ -569,6 +574,10 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size, > { > int ret; > > + ret = security_locked_down(LOCKDOWN_BPF_READ); > + if (ret) > + goto out; > + > /* > * The strncpy_from_unsafe() call will likely not fill the entire > * buffer, but that's okay in this circumstance as we're probing > @@ -579,6 +588,7 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size, > * is returned that can be used for bpf_perf_event_output() et al. > */ > ret = strncpy_from_unsafe(dst, unsafe_ptr, size); > +out: > if (unlikely(ret < 0)) > memset(dst, 0, size); Ditto. Thanks, Daniel
On Mon, Jul 15, 2019 at 3:54 PM Daniel Borkmann <daniel@iogearbox.net> wrote: > Hmm, does security_locked_down() ever return a code > 0 or why do you > have the double check on return code? If not, then for clarity the > ret code from security_locked_down() should be checked as 'ret < 0' > as well and out label should be at the memset directly instead. It doesn't, so I'll update. Thanks!
diff --git a/include/linux/security.h b/include/linux/security.h index 987d8427f091..8dd1741a52cd 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -118,6 +118,7 @@ enum lockdown_reason { LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_KCORE, LOCKDOWN_KPROBES, + LOCKDOWN_BPF_READ, LOCKDOWN_CONFIDENTIALITY_MAX, }; diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index ca1255d14576..605908da61c5 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -142,7 +142,12 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr) { int ret; + ret = security_locked_down(LOCKDOWN_BPF_READ); + if (ret) + goto out; + ret = probe_kernel_read(dst, unsafe_ptr, size); +out: if (unlikely(ret < 0)) memset(dst, 0, size); @@ -569,6 +574,10 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size, { int ret; + ret = security_locked_down(LOCKDOWN_BPF_READ); + if (ret) + goto out; + /* * The strncpy_from_unsafe() call will likely not fill the entire * buffer, but that's okay in this circumstance as we're probing @@ -579,6 +588,7 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size, * is returned that can be used for bpf_perf_event_output() et al. */ ret = strncpy_from_unsafe(dst, unsafe_ptr, size); +out: if (unlikely(ret < 0)) memset(dst, 0, size); diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c index ccb3e9a2a47c..d14b89784412 100644 --- a/security/lockdown/lockdown.c +++ b/security/lockdown/lockdown.c @@ -33,6 +33,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_KCORE] = "/proc/kcore access", [LOCKDOWN_KPROBES] = "use of kprobes", + [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM", [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", };