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selftests: drv-net: ncdevmem: Open /dev/udmabuf O_RDONLY

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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/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>
Link: https://patch.msgid.link/20260722205442.1894665-1-tjmercier@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
T.J. Mercier
2026-07-22 13:54:42 -07:00
committed by Jakub Kicinski
parent 89d8006259
commit be6f0d0bae
1 changed files with 1 additions and 1 deletions
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tools/testing/selftests/drivers/net/hw/ncdevmem.c
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@@ -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;