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Mercier" Cc: kraxel@redhat.com, vivek.kasireddy@intel.com, kuba@kernel.org, Shuah Khan , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH v2] selftests: Open /dev/udmabuf O_RDONLY Message-ID: References: <20260701192210.2997769-1-tjmercier@google.com> Precedence: bulk X-Mailing-List: bpf@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: <20260701192210.2997769-1-tjmercier@google.com> On Wed, Jul 01, 2026 at 12:22:08PM -0700, T.J. Mercier wrote: > Write permissions on the /dev/udmabuf device file are not required to > issue ioctls and allocate udmabufs. Applications should be opening this > file as O_RDONLY. The BPF dmabuf_iter selftest already does this. [1] > > Users are pointing to these selftests as examples of how use udmabuf, > and encountering permission errors on systems where write permissions > are not available on /dev/udmabuf. Apply the principle of least > privilege to selftests which use udmabuf by removing the write access > mode from drivers/dma-buf/udmabuf.c and drivers/net/hw/ncdevmem.c. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c?h=v7.1#n49 > > Signed-off-by: T.J. Mercier > --- > tools/testing/selftests/drivers/dma-buf/udmabuf.c | 2 +- > tools/testing/selftests/drivers/net/hw/ncdevmem.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/tools/testing/selftests/drivers/dma-buf/udmabuf.c b/tools/testing/selftests/drivers/dma-buf/udmabuf.c > index d78aec662586..ced0b95c876c 100644 > --- a/tools/testing/selftests/drivers/dma-buf/udmabuf.c > +++ b/tools/testing/selftests/drivers/dma-buf/udmabuf.c > @@ -140,7 +140,7 @@ int main(int argc, char *argv[]) > ksft_print_header(); > ksft_set_plan(7); > > - devfd = open("/dev/udmabuf", O_RDWR); > + devfd = open("/dev/udmabuf", O_RDONLY); > if (devfd < 0) { > ksft_print_msg( > "%s: [skip,no-udmabuf: Unable to access DMA buffer device file]\n", > diff --git a/tools/testing/selftests/drivers/net/hw/ncdevmem.c b/tools/testing/selftests/drivers/net/hw/ncdevmem.c > index e098d6534c3c..8114a29692fd 100644 > --- a/tools/testing/selftests/drivers/net/hw/ncdevmem.c > +++ b/tools/testing/selftests/drivers/net/hw/ncdevmem.c > @@ -149,7 +149,7 @@ static struct memory_buffer *udmabuf_alloc(size_t size) > > ctx->size = size; > > - ctx->devfd = open("/dev/udmabuf", O_RDWR); > + ctx->devfd = open("/dev/udmabuf", O_RDONLY); > if (ctx->devfd < 0) { > pr_err("[skip,no-udmabuf: Unable to access DMA buffer device file]"); > goto err_free_ctx; > > base-commit: fbb7ad31ab376c5101b2ac7205fad0344fd2de60 > -- > 2.55.0.rc0.799.gd6f94ed593-goog > Reviewed-by: Bobby Eshleman