[PATCH 1/1] udmabuf: reject unknown UDMABUF_CREATE flags

["Iván Ezequiel Rodriguez" <ivanrwcm25@gmail.com>]

UDMABUF_CREATE and UDMABUF_CREATE_LIST only define
UDMABUF_FLAGS_CLOEXEC. Unknown flag bits were silently masked
before returning a dmabuf fd, so userspace could not detect
unsupported flags. Reject them with -EINVAL, consistent with
dma-heap flag validation.

Document the flag semantics in udmabuf.h and add a selftest.

Signed-off-by: Iván Ezequiel Rodriguez <ivanrwcm25@gmail.com>
---
 drivers/dma-buf/udmabuf.c                         |  3 +++
 include/uapi/linux/udmabuf.h                      | 13 +++++++++++++
 tools/testing/selftests/drivers/dma-buf/udmabuf.c | 14 +++++++++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index bced421c0d65..fb36c0d9ffe7 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -358,6 +358,9 @@ static long udmabuf_create(struct miscdevice *device,
 	long ret = -EINVAL;
 	u32 i, flags;
 
+	if (head->flags & ~UDMABUF_FLAGS_CLOEXEC)
+		return -EINVAL;
+
 	ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
 	if (!ubuf)
 		return -ENOMEM;
diff --git a/include/uapi/linux/udmabuf.h b/include/uapi/linux/udmabuf.h
index 46b6532ed855..e267856dd510 100644
--- a/include/uapi/linux/udmabuf.h
+++ b/include/uapi/linux/udmabuf.h
@@ -7,6 +7,13 @@
 
 #define UDMABUF_FLAGS_CLOEXEC	0x01
 
+/**
+ * struct udmabuf_create - parameters for %UDMABUF_CREATE
+ * @memfd: memfd containing the memory to export
+ * @flags: %UDMABUF_FLAGS_CLOEXEC only; unknown bits are rejected
+ * @offset: byte offset into @memfd (page aligned)
+ * @size: number of bytes to export (page aligned, non-zero)
+ */
 struct udmabuf_create {
 	__u32 memfd;
 	__u32 flags;
@@ -21,6 +28,12 @@ struct udmabuf_create_item {
 	__u64 size;
 };
 
+/**
+ * struct udmabuf_create_list - parameters for %UDMABUF_CREATE_LIST
+ * @flags: %UDMABUF_FLAGS_CLOEXEC only; unknown bits are rejected
+ * @count: number of entries in @list (non-zero, capped by driver)
+ * @list: flexible array of memfd regions to combine
+ */
 struct udmabuf_create_list {
 	__u32 flags;
 	__u32 count;
diff --git a/tools/testing/selftests/drivers/dma-buf/udmabuf.c b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
index d78aec662586..95c781855404 100644
--- a/tools/testing/selftests/drivers/dma-buf/udmabuf.c
+++ b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
@@ -138,7 +138,7 @@ int main(int argc, char *argv[])
 	void *addr1, *addr2;
 
 	ksft_print_header();
-	ksft_set_plan(7);
+	ksft_set_plan(8);
 
 	devfd = open("/dev/udmabuf", O_RDWR);
 	if (devfd < 0) {
@@ -189,6 +189,18 @@ int main(int argc, char *argv[])
 	else
 		ksft_test_result_pass("%s: [PASS,test-2]\n", TEST_PREFIX);
 
+	/* should fail (unknown flags) */
+	create.memfd  = memfd;
+	create.offset = 0;
+	create.size   = size;
+	create.flags  = UDMABUF_FLAGS_CLOEXEC | 0x2;
+	buf = ioctl(devfd, UDMABUF_CREATE, &create);
+	if (buf >= 0)
+		ksft_test_result_fail("%s: [FAIL,test-unknown-flags]\n", TEST_PREFIX);
+	else
+		ksft_test_result_pass("%s: [PASS,test-unknown-flags]\n", TEST_PREFIX);
+	create.flags = 0;
+
 	/* should fail (not memfd) */
 	create.memfd  = 0; /* stdin */
 	create.offset = 0;
-- 
2.43.0