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Fri, 19 Jun 2026 14:11:59 -0700 (PDT) Message-ID: <130931685c8b2064325fc65a856ecd810c8a6b5c.camel@gmail.com> Subject: Re: [PATCH bpf v2 2/8] libbpf: ringbuf: Prevent NULL callback crash From: Eduard Zingerman To: Jiri Olsa , Tamir Duberstein Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , 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 Date: Fri, 19 Jun 2026 14:11:56 -0700 In-Reply-To: References: <20260618-bpf-ringbuf-fixes-v2-0-33fde039ddf3@kernel.org> <20260618-bpf-ringbuf-fixes-v2-2-33fde039ddf3@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (3.60.1-1.fc44) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-06-19 at 15:54 +0200, Jiri Olsa wrote: > 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. > >=20 > > 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. Perfo= rm > > both checks before honoring a zero record bound so invalid callback use > > always reports the error. > >=20 > > 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(-) > >=20 > > 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 le= ss), 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); > > =20 > > /** > > - * @brief **ring__consume_n()** consumes up to a requested amount of i= tems from > > - * a ringbuffer without event polling. > > + * @brief **ring__consume_n()** consumes up to a requested number of r= ecords > > + * 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 o= f 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); > > =20 > > 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; > > } > > =20 > > +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 =3D 0; i < rb->ring_cnt; i++) { > > + err =3D 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; > > =20 > > + err =3D ringbuf_validate(r); > > + if (err) > > + return err; >=20 > as Emil noted in first version, this seems like overkill, could you > just check sample_cb !=3D NULL before it's actualy called? >=20 > in [1] you mentioned you plan to add some feature that won't use sample_c= b, > it'd be easier to review/suggest the solution with more details on that >=20 > jirka As-is it appears that the simplest thing to do is to error out in ring_buffer__new() and ring_buffer__add() when callback is NULL or when overwrite map flag is present. I checked our internal usage for then __new/__add functions, and it seems there are no cases when NULL is passed as a callback. [...]