Re: [PATCH v8 2/8] vfio: selftests: Introduce snprintf_assert()

[Vipin Sharma]

On Tue, May 05, 2026 at 09:28:32PM +0000, Raghavendra Rao Ananta wrote:
> Introduce snprintf_assert() to protect the users of snprintf() to fail
> if the requested operation was truncated due to buffer limits. VFIO
> tests and libraries, including a new sysfs library that will be introduced
> by an upcoming patch, rely quite heavily on snprintf()s to build PCI
> sysfs paths. Having a protection against this will be helpful to prevent
> false test failures.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>
> ---
>  .../vfio/lib/include/libvfio/assert.h         |  5 +++++
>  .../selftests/vfio/lib/vfio_pci_device.c      |  8 +++----
>  .../selftests/vfio/vfio_dma_mapping_test.c    |  6 +++---
>  .../selftests/vfio/vfio_pci_device_test.c     | 21 ++++++++++---------
>  4 files changed, 23 insertions(+), 17 deletions(-)
> 
> diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/assert.h b/tools/testing/selftests/vfio/lib/include/libvfio/assert.h
> index f4ebd122d9b6f..77b68c7129a64 100644
> --- a/tools/testing/selftests/vfio/lib/include/libvfio/assert.h
> +++ b/tools/testing/selftests/vfio/lib/include/libvfio/assert.h
> @@ -51,4 +51,9 @@
>  	VFIO_ASSERT_EQ(__ret, 0, "ioctl(%s, %s, %s) returned %d\n", #_fd, #_op, #_arg, __ret); \
>  } while (0)
>  
> +#define snprintf_assert(_s, _size, _fmt, ...) do {                      \
> +	int __ret = snprintf(_s, _size, _fmt, ##__VA_ARGS__);           \
> +	VFIO_ASSERT_LT(__ret, _size);                                   \
> +} while (0)
> +
>  #endif /* SELFTESTS_VFIO_LIB_INCLUDE_LIBVFIO_ASSERT_H */
> diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> index fc75e04ef010c..efbf9ab63cea7 100644
> --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> @@ -211,7 +211,7 @@ static unsigned int vfio_pci_get_group_from_dev(const char *bdf)
>  	unsigned int group;
>  	int ret;
>  
> -	snprintf(sysfs_path, PATH_MAX, "%s/%s/iommu_group", PCI_SYSFS_PATH, bdf);
> +	snprintf_assert(sysfs_path, PATH_MAX, "%s/%s/iommu_group", PCI_SYSFS_PATH, bdf);
>  
>  	ret = readlink(sysfs_path, dev_iommu_group_path, sizeof(dev_iommu_group_path));
>  	VFIO_ASSERT_NE(ret, -1, "Failed to get the IOMMU group for device: %s\n", bdf);
> @@ -231,7 +231,7 @@ static void vfio_pci_group_setup(struct vfio_pci_device *device, const char *bdf
>  	int group;
>  
>  	group = vfio_pci_get_group_from_dev(bdf);
> -	snprintf(group_path, sizeof(group_path), "/dev/vfio/%d", group);
> +	snprintf_assert(group_path, sizeof(group_path), "/dev/vfio/%d", group);
>  
>  	device->group_fd = open(group_path, O_RDWR);
>  	VFIO_ASSERT_GE(device->group_fd, 0, "open(%s) failed\n", group_path);
> @@ -302,7 +302,7 @@ const char *vfio_pci_get_cdev_path(const char *bdf)
>  	cdev_path = calloc(PATH_MAX, 1);
>  	VFIO_ASSERT_NOT_NULL(cdev_path);
>  
> -	snprintf(dir_path, sizeof(dir_path), "/sys/bus/pci/devices/%s/vfio-dev/", bdf);
> +	snprintf_assert(dir_path, sizeof(dir_path), "/sys/bus/pci/devices/%s/vfio-dev/", bdf);
>  
>  	dir = opendir(dir_path);
>  	VFIO_ASSERT_NOT_NULL(dir, "Failed to open directory %s\n", dir_path);
> @@ -312,7 +312,7 @@ const char *vfio_pci_get_cdev_path(const char *bdf)
>  		if (strncmp("vfio", entry->d_name, 4))
>  			continue;
>  
> -		snprintf(cdev_path, PATH_MAX, "/dev/vfio/devices/%s", entry->d_name);
> +		snprintf_assert(cdev_path, PATH_MAX, "/dev/vfio/devices/%s", entry->d_name);
>  		break;
>  	}
>  
> diff --git a/tools/testing/selftests/vfio/vfio_dma_mapping_test.c b/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> index abb170bdcef7e..7d0de8c79de13 100644
> --- a/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> +++ b/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> @@ -44,9 +44,9 @@ static int intel_iommu_mapping_get(const char *bdf, u64 iova,
>  	FILE *file;
>  	char *rest;
>  
> -	snprintf(iommu_mapping_path, sizeof(iommu_mapping_path),
> -		 "/sys/kernel/debug/iommu/intel/%s/domain_translation_struct",
> -		 bdf);
> +	snprintf_assert(iommu_mapping_path, sizeof(iommu_mapping_path),
> +			"/sys/kernel/debug/iommu/intel/%s/domain_translation_struct",
> +			bdf);
>  
>  	printf("Searching for IOVA 0x%lx in %s\n", iova, iommu_mapping_path);
>  
> diff --git a/tools/testing/selftests/vfio/vfio_pci_device_test.c b/tools/testing/selftests/vfio/vfio_pci_device_test.c
> index 7c0fe8ce3a61f..93c11fd5e0818 100644
> --- a/tools/testing/selftests/vfio/vfio_pci_device_test.c
> +++ b/tools/testing/selftests/vfio/vfio_pci_device_test.c
> @@ -39,16 +39,17 @@ FIXTURE_TEARDOWN(vfio_pci_device_test)
>  	iommu_cleanup(self->iommu);
>  }
>  
> -#define read_pci_id_from_sysfs(_file) ({							\
> -	char __sysfs_path[PATH_MAX];								\
> -	char __buf[32];										\
> -	int __fd;										\
> -												\
> -	snprintf(__sysfs_path, PATH_MAX, "/sys/bus/pci/devices/%s/%s", device_bdf, _file);	\
> -	ASSERT_GT((__fd = open(__sysfs_path, O_RDONLY)), 0);					\
> -	ASSERT_GT(read(__fd, __buf, ARRAY_SIZE(__buf)), 0);					\
> -	ASSERT_EQ(0, close(__fd));								\
> -	(u16)strtoul(__buf, NULL, 0);								\
> +#define read_pci_id_from_sysfs(_file) ({					\
> +	char __sysfs_path[PATH_MAX];						\
> +	char __buf[32];								\
> +	int __fd;								\
> +										\
> +	snprintf_assert(__sysfs_path, PATH_MAX, "/sys/bus/pci/devices/%s/%s",	\
> +			device_bdf, _file);					\
> +	ASSERT_GT((__fd = open(__sysfs_path, O_RDONLY)), 0);			\
> +	ASSERT_GT(read(__fd, __buf, ARRAY_SIZE(__buf)), 0);			\
> +	ASSERT_EQ(0, close(__fd));						\
> +	(u16)strtoul(__buf, NULL, 0);						\
>  })
>  
>  TEST_F(vfio_pci_device_test, config_space_read_write)
> -- 
> 2.54.0.545.g6539524ca2-goog
> 
Reviewed-by: Vipin Sharma <vipinsh@xxxxxxxxxx>