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