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[35.205.88.202]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-388c80121d4sm8996562f8f.2.2024.12.16.09.54.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Dec 2024 09:54:47 -0800 (PST) Date: Mon, 16 Dec 2024 17:54:43 +0000 From: Vincent Donnefort To: Jeongjun Park Cc: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, david@redhat.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH] ring-buffer: fix array bounds checking Message-ID: References: <20241216164931.57323-1-aha310510@gmail.com> 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: <20241216164931.57323-1-aha310510@gmail.com> On Tue, Dec 17, 2024 at 01:49:30AM +0900, Jeongjun Park wrote: > If there is a case where the variable s is greater than or equal to nr_subbufs > before entering the loop, oob read or use-after-free will occur. This problem > occurs because the variable s is used as an index to dereference the > struct page before the variable value range check. This logic prevents the > wrong address value from being copied to the pages array through the subsequent > range check, but oob read still occurs, so the code needs to be modified. Hi Jeongjun, thanks for the patch. Did you find a reproducer for that problem or has it just been found by code inspection? As discussed here [1], s >= nr_subbufs should really never happen as we already cap nr_pages. [1] https://lore.kernel.org/all/78e20e98-bdfc-4d7b-a59c-988b81fcc58b@redhat.com/, > > Fixes: 117c39200d9d ("ring-buffer: Introducing ring-buffer mapping functions") > Signed-off-by: Jeongjun Park > --- > kernel/trace/ring_buffer.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 7e257e855dd1..83da74bf7bd6 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -6994,9 +6994,9 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, > { > unsigned long nr_subbufs, nr_pages, nr_vma_pages, pgoff = vma->vm_pgoff; > unsigned int subbuf_pages, subbuf_order; > - struct page **pages; > + struct page **pages, *page; > int p = 0, s = 0; > - int err; > + int err, off; > > /* Refuse MP_PRIVATE or writable mappings */ > if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC || > @@ -7055,14 +7055,14 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, > } > > while (p < nr_pages) { > - struct page *page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]); > - int off = 0; > - I believe we can keep the struct page and off declaration within the while loop. > if (WARN_ON_ONCE(s >= nr_subbufs)) { > err = -EINVAL; > goto out; > } > > + page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]); > + off = 0; > + > for (; off < (1 << (subbuf_order)); off++, page++) { > if (p >= nr_pages) > break; > --