Hello T J,

On Wed, 12 Aug 2026 at 02:11, T.J. Mercier tjmercier@google.com wrote:

Write permissions on the /dev/dma_heap/* device files are not required to issue ioctls and allocate dmabufs. Applications should be opening these file as O_RDONLY. The BPF dmabuf_iter selftest already does this. [1]

Users are pointing to these selftests as examples of how use dmabuf, and encountering permission errors on systems where write permissions are not available on /dev/dma_heap/*. Apply the principle of least privilege to selftests which open dmabuf heaps by removing the write access mode and using O_RDONLY for the open() instead.

Thanks for the patch.

The same is true for the vgem test using /dev/dri/card.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tool...

Signed-off-by: T.J. Mercier tjmercier@google.com

Acked-by: Sumit Semwal sumit.semwal@linaro.org

---

tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c index fc9694fc4e89..45b420e37c97 100644 --- a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c +++ b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c @@ -48,7 +48,7 @@ static int open_vgem(void)

            snprintf(name, 80, "%s%u", drmstr, i);

•           fd = open(name, O_RDWR);
  

•           fd = open(name, O_RDONLY);
            if (fd < 0)
                    continue;
  
  

@@ -96,7 +96,7 @@ static int dmabuf_heap_open(char *name) if (ret < 0) ksft_exit_fail_msg("snprintf failed! %d\n", ret);

•   fd = open(buf, O_RDWR);
  

•   fd = open(buf, O_RDONLY);
    if (fd < 0)
            ksft_exit_fail_msg("open %s failed: %s\n", buf, strerror(errno));
  
  
  

base-commit: 9a11db68872055e6ead919bad04d6330851c522d

2.55.0.679.g6767b8d81c-goog