fprobe: add recursion detection in fprobe_exit_handler

fprobe_hander and fprobe_kprobe_handler has guarded ftrace recursion
detection but fprobe_exit_handler has not, which possibly introduce
recursive calls if the fprobe exit callback calls any traceable
functions. Checking in fprobe_hander or fprobe_kprobe_handler
is not enough and misses this case.

So add recursion free guard the same way as fprobe_hander. Since
ftrace recursion check does not employ ip(s), so here use entry_ip and
entry_parent_ip the same as fprobe_handler.

Link: https://lore.kernel.org/all/[email protected]/

Fixes: 5b0ab78 ("fprobe: Add exit_handler support")
Signed-off-by: Ze Gao <[email protected]>
Cc: [email protected]
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>

Author: zegao96

kernel/trace/fprobe.c

@@ -17,6 +17,7 @@
 struct fprobe_rethook_node {
 	struct rethook_node node;
 	unsigned long entry_ip;
+	unsigned long entry_parent_ip;
 	char data[];
 };
 
@@ -39,6 +40,7 @@ static inline void __fprobe_handler(unsigned long ip, unsigned long parent_ip,
 		}
 		fpr = container_of(rh, struct fprobe_rethook_node, node);
 		fpr->entry_ip = ip;
+		fpr->entry_parent_ip = parent_ip;
 		if (fp->entry_data_size)
 			entry_data = fpr->data;
 	}
@@ -114,14 +116,26 @@ static void fprobe_exit_handler(struct rethook_node *rh, void *data,
 {
 	struct fprobe *fp = (struct fprobe *)data;
 	struct fprobe_rethook_node *fpr;
+	int bit;
 
 	if (!fp || fprobe_disabled(fp))
 		return;
 
 	fpr = container_of(rh, struct fprobe_rethook_node, node);
 
+	/*
+	 * we need to assure no calls to traceable functions in-between the
+	 * end of fprobe_handler and the beginning of fprobe_exit_handler.
+	 */
+	bit = ftrace_test_recursion_trylock(fpr->entry_ip, fpr->entry_parent_ip);
+	if (bit < 0) {
+		fp->nmissed++;
+		return;
+	}
+
 	fp->exit_handler(fp, fpr->entry_ip, regs,
 			 fp->entry_data_size ? (void *)fpr->data : NULL);
+	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(fprobe_exit_handler);