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Fri, 19 Jun 2026 06:55:01 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Fri, 19 Jun 2026 15:54:59 +0200 To: Tamir Duberstein Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Shuah Khan , Andrea Righi , Xu Kuohai , Andrea Righi , Bing-Jhong Billy Jheng , David Vernet , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Werner , Zvi Effron , Andrii Nakryiko , Emil Tsalapatis Subject: Re: [PATCH bpf v2 2/8] libbpf: ringbuf: Prevent NULL callback crash Message-ID: References: <20260618-bpf-ringbuf-fixes-v2-0-33fde039ddf3@kernel.org> <20260618-bpf-ringbuf-fixes-v2-2-33fde039ddf3@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260618-bpf-ringbuf-fixes-v2-2-33fde039ddf3@kernel.org> On Thu, Jun 18, 2026 at 08:26:40PM -0400, Tamir Duberstein wrote: > ring_buffer__new() and ring_buffer__add() allow a NULL sample > callback. When callback-based consumption reaches such a ring, it calls > through the NULL function pointer and crashes. > > Check every ring before manager polling or consumption so a missing > callback returns -EINVAL before the manager waits or consumes another > ring. Check the selected ring before direct per-ring consumption. Perform > both checks before honoring a zero record bound so invalid callback use > always reports the error. > > Fixes: bf99c936f947 ("libbpf: Add BPF ring buffer support") > Assisted-by: Codex:gpt-5.5 > Signed-off-by: Tamir Duberstein > --- > tools/lib/bpf/libbpf.h | 11 ++- > tools/lib/bpf/ringbuf.c | 43 +++++++++-- > tools/testing/selftests/bpf/prog_tests/ringbuf.c | 93 ++++++++++++++++++++++++ > 3 files changed, 136 insertions(+), 11 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > index bba4e8464396..9ba6b9ad3498 100644 > --- a/tools/lib/bpf/libbpf.h > +++ b/tools/lib/bpf/libbpf.h > @@ -1526,18 +1526,17 @@ LIBBPF_API int ring__map_fd(const struct ring *r); > * > * @param r A ringbuffer object. > * @return The number of records consumed (or INT_MAX, whichever is less), or > - * a negative number if any of the callbacks return an error. > + * a negative error code on failure. > */ > LIBBPF_API int ring__consume(struct ring *r); > > /** > - * @brief **ring__consume_n()** consumes up to a requested amount of items from > - * a ringbuffer without event polling. > + * @brief **ring__consume_n()** consumes up to a requested number of records > + * from a ringbuffer without event polling. > * > * @param r A ringbuffer object. > - * @param n Maximum amount of items to consume. > - * @return The number of items consumed, or a negative number if any of the > - * callbacks return an error. > + * @param n Maximum number of records to consume. > + * @return The number of records consumed, or a negative error code on failure. > */ > LIBBPF_API int ring__consume_n(struct ring *r, size_t n); > > diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c > index f2bb619d5a75..0dae4d95d309 100644 > --- a/tools/lib/bpf/ringbuf.c > +++ b/tools/lib/bpf/ringbuf.c > @@ -231,6 +231,26 @@ static inline int roundup_len(__u32 len) > return (len + 7) / 8 * 8; > } > > +static int ringbuf_validate(const struct ring *r) > +{ > + if (unlikely(!r->sample_cb)) > + return -EINVAL; > + return 0; > +} > + > +static int ringbuf_validate_callbacks(const struct ring_buffer *rb) > +{ > + int i, err; > + > + for (i = 0; i < rb->ring_cnt; i++) { > + err = ringbuf_validate(rb->rings[i]); > + if (err) > + return err; > + } > + > + return 0; > +} > + > static int64_t ringbuf_process_ring(struct ring *r, size_t n) > { > int *len_ptr, len, err; > @@ -240,6 +260,9 @@ static int64_t ringbuf_process_ring(struct ring *r, size_t n) > bool got_new_data; > void *sample; > > + err = ringbuf_validate(r); > + if (err) > + return err; as Emil noted in first version, this seems like overkill, could you just check sample_cb != NULL before it's actualy called? in [1] you mentioned you plan to add some feature that won't use sample_cb, it'd be easier to review/suggest the solution with more details on that jirka [1] https://lore.kernel.org/bpf/e384ef2f478093a70af11980d2d1cdeb@kernel.org/