chase: put limit on overall chase cycles

Let's add some protections in case we deal with inodes owned by an
untrusted person, with concurrent access: let's put a limit on how long
we traverse, and fail eventually so that live changes cannot send us in
circles indefinitely.

This reworks the current CHASE_MAX logic so that it not only applies to
symlinks transitions, but to any transitions.

This also bumps CHASE_MAX a bit, given that it's now bumped on every
single iteration of the loop.

src/basic/chase.h

@@ -35,7 +35,7 @@ typedef enum ChaseFlags {
 bool unsafe_transition(const struct stat *a, const struct stat *b);
 
 /* How many iterations to execute before returning -ELOOP */
-#define CHASE_MAX 32
+#define CHASE_MAX 128U
 
 int chase(const char *path_with_prefix, const char *root, ChaseFlags flags, char **ret_path, int *ret_fd);