tracepoint: Add tracepoint_probe_register_may_exist() for BPF tracing

commit 9913d5745bd720c4266805c8d29952a3702e4eca upstream.

All internal use cases for tracepoint_probe_register() is set to not ever
be called with the same function and data. If it is, it is considered a
bug, as that means the accounting of handling tracepoints is corrupted.
If the function and data for a tracepoint is already registered when
tracepoint_probe_register() is called, it will call WARN_ON_ONCE() and
return with EEXISTS.

The BPF system call can end up calling tracepoint_probe_register() with
the same data, which now means that this can trigger the warning because
of a user space process. As WARN_ON_ONCE() should not be called because
user space called a system call with bad data, there needs to be a way to
register a tracepoint without triggering a warning.

Enter tracepoint_probe_register_may_exist(), which can be called, but will
not cause a WARN_ON() if the probe already exists. It will still error out
with EEXIST, which will then be sent to the user space that performed the
BPF system call.

This keeps the previous testing for issues with other users of the
tracepoint code, while letting BPF call it with duplicated data and not
warn about it.

Link: https://lore.kernel.org/lkml/20210626135845.4080-1-penguin-kernel@I-love.SAKURA.ne.jp/
Link: https://syzkaller.appspot.com/bug?id=41f4318cf01762389f4d1c1c459da4f542fe5153
Cc: stable@vger.kernel.org
Fixes: c4f6699dfcb85 ("bpf: introduce BPF_RAW_TRACEPOINT")
Reported-by: syzbot <syzbot+721aa903751db87aa244@syzkaller.appspotmail.com>
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot+721aa903751db87aa244@syzkaller.appspotmail.com
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 966ed898032746b58ad79caead930f66292a9148..e4c5df71f0e7479834f7e55e8f1c12e6fa9331a0 100644 (file)
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -41,7 +41,17 @@ extern int
 tracepoint_probe_register_prio(struct tracepoint *tp, void *probe, void *data,
                               int prio);
 extern int
+tracepoint_probe_register_prio_may_exist(struct tracepoint *tp, void *probe, void *data,
+                                        int prio);
+extern int
 tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data);
+static inline int
+tracepoint_probe_register_may_exist(struct tracepoint *tp, void *probe,
+                                   void *data)
+{
+       return tracepoint_probe_register_prio_may_exist(tp, probe, data,
+                                                       TRACEPOINT_DEFAULT_PRIO);
+}
 extern void
 for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
                void *priv);

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 01710831fd02fc1652fca87c01d57782358a2ae1..216329c23f18aca189fefd4718a31ef16e589592 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2106,7 +2106,8 @@ static int __bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *
        if (prog->aux->max_tp_access > btp->writable_size)
                return -EINVAL;
 
-       return tracepoint_probe_register(tp, (void *)btp->bpf_func, prog);
+       return tracepoint_probe_register_may_exist(tp, (void *)btp->bpf_func,
+                                                  prog);
 }
 
 int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *prog)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 3e261482296cf2c13d03cdf4d5c66bb959baf6f6..f8b161edca5eaa6e5869d202694fb362aeb42020 100644 (file)
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -294,7 +294,8 @@ static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func
  * Add the probe function to a tracepoint.
  */
 static int tracepoint_add_func(struct tracepoint *tp,
-                              struct tracepoint_func *func, int prio)
+                              struct tracepoint_func *func, int prio,
+                              bool warn)
 {
        struct tracepoint_func *old, *tp_funcs;
        int ret;
@@ -309,7 +310,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
                        lockdep_is_held(&tracepoints_mutex));
        old = func_add(&tp_funcs, func, prio);
        if (IS_ERR(old)) {
-               WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
+               WARN_ON_ONCE(warn && PTR_ERR(old) != -ENOMEM);
                return PTR_ERR(old);
        }
 
@@ -364,6 +365,32 @@ static int tracepoint_remove_func(struct tracepoint *tp,
        return 0;
 }
 
+/**
+ * tracepoint_probe_register_prio_may_exist -  Connect a probe to a tracepoint with priority
+ * @tp: tracepoint
+ * @probe: probe handler
+ * @data: tracepoint data
+ * @prio: priority of this function over other registered functions
+ *
+ * Same as tracepoint_probe_register_prio() except that it will not warn
+ * if the tracepoint is already registered.
+ */
+int tracepoint_probe_register_prio_may_exist(struct tracepoint *tp, void *probe,
+                                            void *data, int prio)
+{
+       struct tracepoint_func tp_func;
+       int ret;
+
+       mutex_lock(&tracepoints_mutex);
+       tp_func.func = probe;
+       tp_func.data = data;
+       tp_func.prio = prio;
+       ret = tracepoint_add_func(tp, &tp_func, prio, false);
+       mutex_unlock(&tracepoints_mutex);
+       return ret;
+}
+EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio_may_exist);
+
 /**
  * tracepoint_probe_register_prio -  Connect a probe to a tracepoint with priority
  * @tp: tracepoint
@@ -387,7 +414,7 @@ int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
        tp_func.func = probe;
        tp_func.data = data;
        tp_func.prio = prio;
-       ret = tracepoint_add_func(tp, &tp_func, prio);
+       ret = tracepoint_add_func(tp, &tp_func, prio, true);
        mutex_unlock(&tracepoints_mutex);
        return ret;
 }