[PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY

[PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY

[T.J. Mercier]

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.

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/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c?h=v7.1#n49

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

Re: [PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY

[John Stultz]

On Tue, Aug 11, 2026 at 1:41 PM 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.
>
> 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/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c?h=v7.1#n49
>
> Signed-off-by: T.J. Mercier <tjmercier@google.com>

Acked-by: John Stultz <jstultz@google.com>

thanks
-john

Re: [PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY

[Christian König]

On 8/11/26 22:41, T.J. Mercier 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.
> 
> 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/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c?h=v7.1#n49
> 
> Signed-off-by: T.J. Mercier <tjmercier@google.com>

Acked-by: Christian König <christian.koenig@amd.com>

> ---
>  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