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Subject[PATCH v2] kprobes: avoid the kprobe being re-registered
Date
Changes from v1:
- We should put the modifies of the kprobe after the re-reg check.
- And then the address_safe check.
- When check_kprobe_address_safe() return fail, the *probed_mod
should be set to NULL, and no module refcount held.

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.

Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com>
---
kernel/kprobes.c | 28 +++++++++-------------------
1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index a1606a4..f622639 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;
@@ -1501,6 +1488,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
* its code to prohibit unexpected unloading.
*/
if (unlikely(!try_module_get(*probed_mod))) {
+ *probed_mod = NULL;
ret = -ENOENT;
goto out;
}
@@ -1536,9 +1524,13 @@ 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 +1539,7 @@ 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
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