lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 8 May 2020 22:30:41 -0700 From: Alexei Starovoitov <ast@...com> To: Yonghong Song <yhs@...com>, Andrii Nakryiko <andrii.nakryiko@...il.com> CC: Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>, Martin KaFai Lau <kafai@...com>, Networking <netdev@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>, Kernel Team <kernel-team@...com> Subject: Re: [PATCH bpf-next v3 13/21] bpf: add bpf_seq_printf and bpf_seq_write helpers On 5/8/20 9:18 PM, Yonghong Song wrote: > > > On 5/8/20 12:44 PM, Andrii Nakryiko wrote: >> On Wed, May 6, 2020 at 10:40 PM Yonghong Song <yhs@...com> wrote: >>> >>> Two helpers bpf_seq_printf and bpf_seq_write, are added for >>> writing data to the seq_file buffer. >>> >>> bpf_seq_printf supports common format string flag/width/type >>> fields so at least I can get identical results for >>> netlink and ipv6_route targets. >>> >>> For bpf_seq_printf and bpf_seq_write, return value -EOVERFLOW >>> specifically indicates a write failure due to overflow, which >>> means the object will be repeated in the next bpf invocation >>> if object collection stays the same. Note that if the object >>> collection is changed, depending how collection traversal is >>> done, even if the object still in the collection, it may not >>> be visited. >>> >>> bpf_seq_printf may return -EBUSY meaning that internal percpu >>> buffer for memory copy of strings or other pointees is >>> not available. Bpf program can return 1 to indicate it >>> wants the same object to be repeated. Right now, this should not >>> happen on no-RT kernels since migrate_disable(), which guards >>> bpf prog call, calls preempt_disable(). >>> >>> Signed-off-by: Yonghong Song <yhs@...com> >>> --- >>> include/uapi/linux/bpf.h | 32 +++++- >>> kernel/trace/bpf_trace.c | 200 +++++++++++++++++++++++++++++++++ >>> scripts/bpf_helpers_doc.py | 2 + >>> tools/include/uapi/linux/bpf.h | 32 +++++- >>> 4 files changed, 264 insertions(+), 2 deletions(-) >>> >> >> Was a bit surprised by behavior on failed memory read, I think it's >> important to emphasize and document this. But otherwise: >> >> Acked-by: Andrii Nakryiko <andriin@...com> >> >> [...] >> >>> + if (fmt[i] == 's') { >>> + /* try our best to copy */ >>> + if (memcpy_cnt >= MAX_SEQ_PRINTF_MAX_MEMCPY) { >>> + err = -E2BIG; >>> + goto out; >>> + } >>> + >>> + bufs->buf[memcpy_cnt][0] = 0; >>> + strncpy_from_unsafe(bufs->buf[memcpy_cnt], >>> + (void *) (long) >>> args[fmt_cnt], >>> + MAX_SEQ_PRINTF_STR_LEN); >> >> So the behavior is that we try to read string, but if it fails, we >> treat it as empty string? That needs to be documented, IMHO. My >> expectation was that entire printf would fail. > > Let me return proper error. Currently, two possible errors may happen: > - user provide an invalid address, yes, an error should be returned > and we should not do anything > - user provide a valid address, but it needs page fault happening > to read the content. With current implementation, > strncpy_from_unsafe will return fail. Future sleepable > bpf program will help for this case, so an error means a > real address error. It matches what bpf_trace_printk() is doing. I suggest to defer any improvements to later patches. Both should be consistent.
Powered by blists - more mailing lists