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 <[email protected]> > --- > 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 <[email protected]>
