tools/gethostlatency,slabratetop: read strings with bpf_probe_read_*_str

The BCC versions have the same defect as the libbpf-tools versions: the host argument and the slab cache name are read with the fixed-size bpf_probe_read_user()/bpf_probe_read_kernel() helpers, which copy past the source string's NUL terminator and leak adjacent memory into the map value and perf output.

Use the NUL-stopping *_str variants so only the string is copied into the zero-initialized destination.

Author: vdasu

tools/gethostlatency.py

@@ -66,7 +66,7 @@
     u32 tid = (u32)pid_tgid;
 
     if (bpf_get_current_comm(&val.comm, sizeof(val.comm)) == 0) {
-        bpf_probe_read_user(&val.host, sizeof(val.host),
+        bpf_probe_read_user_str(&val.host, sizeof(val.host),
                        (void *)PT_REGS_PARM1(ctx));
         val.pid = pid;
         val.ts = bpf_ktime_get_ns();

tools/slabratetop.py

@@ -186,7 +186,7 @@
 {
     struct info_t info = {};
     const char *name = cachep->name;
-    bpf_probe_read_kernel(&info.name, sizeof(info.name), name);
+    bpf_probe_read_kernel_str(&info.name, sizeof(info.name), name);
 
     struct val_t *valp, zero = {};
     valp = counts.lookup_or_try_init(&info, &zero);