iommufd/selftest: Add missing close(mfd) in memfd_mmap()

Do not forget to close mfd in the error paths, since none of the callers
would close it when ASSERT_NE(MAP_FAILED, buf) fails.

Fixes: 0bcceb1 ("iommufd: Selftest coverage for IOMMU_IOAS_MAP_FILE")
Link: https://patch.msgid.link/r/a363a69dbf453d4bc1bde276f3b16778620488e1.1750787928.git.nicolinc@nvidia.com
Cc: stable@vger.kernel.org
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: nicolinc

tools/testing/selftests/iommu/iommufd_utils.h

@@ -60,13 +60,18 @@ static inline void *memfd_mmap(size_t length, int prot, int flags, int *mfd_p)
 {
 	int mfd_flags = (flags & MAP_HUGETLB) ? MFD_HUGETLB : 0;
 	int mfd = memfd_create("buffer", mfd_flags);
+	void *buf = MAP_FAILED;
 
 	if (mfd <= 0)
 		return MAP_FAILED;
 	if (ftruncate(mfd, length))
-		return MAP_FAILED;
+		goto out;
 	*mfd_p = mfd;
-	return mmap(0, length, prot, flags, mfd, 0);
+	buf = mmap(0, length, prot, flags, mfd, 0);
+out:
+	if (buf == MAP_FAILED)
+		close(mfd);
+	return buf;
 }
 
 /*