[PATCH v7 2/8] vfio: selftests: Introduce snprintf_assert()

Raghavendra Rao Ananta
2026-04-02T17:31:05Z

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@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
---
.../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 4e5871f1ebc3b..1538d2b30ae59 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -209,7 +209,7 @@ 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);
@@ -229,7 +229,7 @@ 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);
@@ -300,7 +300,7 @@ 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);
@@ -310,7 +310,7 @@ 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)
--
2.53.0.1213.gd9a14994de-goog