[PATCH net-next] selftests: drv-net: ncdevmem: Open /dev/udmabuf O_RDONLY

[PATCH net-next] selftests: drv-net: ncdevmem: Open /dev/udmabuf O_RDONLY

[T.J. Mercier]

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 <tjmercier@google.com>
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
 tools/testing/selftests/drivers/net/hw/ncdevmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/drivers/net/hw/ncdevmem.c b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
index d96e8a3b5a65..ffe1d5c1fa4e 100644
--- a/tools/testing/selftests/drivers/net/hw/ncdevmem.c
+++ b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
@@ -150,7 +150,7 @@ 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;
-- 
2.55.0.229.g6434b31f56-goog

Re: [PATCH net-next] selftests: drv-net: ncdevmem: Open /dev/udmabuf O_RDONLY

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 22 Jul 2026 13:54:42 -0700 you 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.
> 
> [...]

Here is the summary with links:
  - [net-next] selftests: drv-net: ncdevmem: Open /dev/udmabuf O_RDONLY
    https://git.kernel.org/netdev/net-next/c/be6f0d0bae22

You are awesome, thank you!
-- 
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