[PATCH v9 10/11] samples/landlock: Extend sample tool to support LANDLOCK_ACCESS_FS_TRUNCATE

[Günther Noack]

Update the sandboxer sample to restrict truncate actions. This is
automatically enabled by default if the running kernel supports
LANDLOCK_ACCESS_FS_TRUNCATE, except for the paths listed in the
LL_FS_RW environment variable.

Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
---
 samples/landlock/sandboxer.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index f29bb3c72230..fd4237c64fb2 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -76,7 +76,8 @@ static int parse_path(char *env_path, const char ***const path_list)
 #define ACCESS_FILE ( \
 	LANDLOCK_ACCESS_FS_EXECUTE | \
 	LANDLOCK_ACCESS_FS_WRITE_FILE | \
-	LANDLOCK_ACCESS_FS_READ_FILE)
+	LANDLOCK_ACCESS_FS_READ_FILE | \
+	LANDLOCK_ACCESS_FS_TRUNCATE)
 
 /* clang-format on */
 
@@ -160,11 +161,12 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
 	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
 	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
 	LANDLOCK_ACCESS_FS_MAKE_SYM | \
-	LANDLOCK_ACCESS_FS_REFER)
+	LANDLOCK_ACCESS_FS_REFER | \
+	LANDLOCK_ACCESS_FS_TRUNCATE)
 
 /* clang-format on */
 
-#define LANDLOCK_ABI_LAST 2
+#define LANDLOCK_ABI_LAST 3
 
 int main(const int argc, char *const argv[], char *const *const envp)
 {
@@ -234,6 +236,10 @@ int main(const int argc, char *const argv[], char *const *const envp)
 	case 1:
 		/* Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 */
 		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
+		__attribute__((fallthrough));
+	case 2:
+		/* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
+		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
 
 		fprintf(stderr,
 			"Hint: You should update the running kernel "
-- 
2.38.0