[PATCH v3 1/2] kprobes: avoid the kprobe being re-registered

[Zhou Chengming]

Changes:
- We should put the modifies of the kprobe after the re-reg check.
- And then the address_safe check.

Old code use check_kprobe_rereg() to check if the kprobe has been
registered already, but check_kprobe_rereg() will release the
kprobe_mutex then, so maybe two paths will pass the check and
register the same kprobe. This patch put the check inside the mutex.

Suggested-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Zhou Chengming <zhouchengming1@xxxxxxxxxx>
---
 kernel/kprobes.c | 27 ++++++++-------------------
 1 file changed, 8 insertions(+), 19 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index a1606a4..1eeedac 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1443,19 +1443,6 @@ static struct kprobe *__get_valid_kprobe(struct kprobe *p)
 	return ap;
 }
 
-/* Return error if the kprobe is being re-registered */
-static inline int check_kprobe_rereg(struct kprobe *p)
-{
-	int ret = 0;
-
-	mutex_lock(&kprobe_mutex);
-	if (__get_valid_kprobe(p))
-		ret = -EINVAL;
-	mutex_unlock(&kprobe_mutex);
-
-	return ret;
-}
-
 int __weak arch_check_ftrace_location(struct kprobe *p)
 {
 	unsigned long ftrace_addr;
@@ -1536,9 +1523,13 @@ int register_kprobe(struct kprobe *p)
 		return PTR_ERR(addr);
 	p->addr = addr;
 
-	ret = check_kprobe_rereg(p);
-	if (ret)
-		return ret;
+	mutex_lock(&kprobe_mutex);
+
+	/* Return error if the kprobe is being re-registered */
+	if (__get_valid_kprobe(p)) {
+		ret = -EINVAL;
+		goto out;
+	}
 
 	/* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
 	p->flags &= KPROBE_FLAG_DISABLED;
@@ -1547,9 +1538,7 @@ int register_kprobe(struct kprobe *p)
 
 	ret = check_kprobe_address_safe(p, &probed_mod);
 	if (ret)
-		return ret;
-
-	mutex_lock(&kprobe_mutex);
+		goto out;
 
 	old_p = get_kprobe(p->addr);
 	if (old_p) {
-- 
1.8.3.1