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

T.J. Mercier posted 1 patch 1 month, 2 weeks ago 
tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
[PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY
Posted by T.J. Mercier 1 month, 2 weeks ago 
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
Posted by Sumit Semwal 1 month, 2 weeks ago 
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/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c?h=v7.1#n49
>
> 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
>
Re: [PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY
Posted by T.J. Mercier 1 month, 2 weeks ago 
On Wed, Aug 12, 2026 at 8:02 AM Sumit Semwal <sumit.semwal@linaro.org> wrote:
>
> 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/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c?h=v7.1#n49
> >
> > Signed-off-by: T.J. Mercier <tjmercier@google.com>
> Acked-by: Sumit Semwal <sumit.semwal@linaro.org>

Thanks for the quick revieews John, Christian, and Sumit!
Re: [PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY
Posted by Christian König 1 month, 2 weeks ago 
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
Re: [PATCH] kselftests: dmabuf-heaps: Open heap device files O_RDONLY
Posted by John Stultz 1 month, 2 weeks ago 
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

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