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Date:   Wed, 25 Oct 2017 20:29:12 +0800
From:   Bixuan Cui <cuibixuan@...wei.com>
To:     <linux-kernel@...r.kernel.org>
CC:     "Libin (Huawei)" <huawei.libin@...wei.com>,
        "kangwen (A)" <kangwen1@...wei.com>
Subject: [PATCH] kernel/kprobes: add check to avoid memory leaks

The register_kretprobe(struct kretprobe *rp) creates and initializes
a hash list for rp->free_instances when register kretprobe every time.
Then malloc memory for it.

The test case:
static struct kretprobe rp;
struct  kretprobe *rps[2]={&rp, &rp};
static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{
        printk(KERN_DEBUG "ret_handler\n");
        return 0;
}
static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{
        printk(KERN_DEBUG "entry_handler\n");
        return 0;
}
static int __init kretprobe_init(void)
{
        int ret;
        rp.kp.addr = (kprobe_opcode_t *)kallsyms_lookup_name("do_fork");
        rp.handler=ret_handler;
        rp.entry_handler=entry_handler;
        rp.maxactive = 3;

        ret = register_kretprobes(rps,2);

Result:
unreferenced object 0xffff8010b12ad980 (size 64):
comm "insmod", pid 17352, jiffies 4298977824 (age 63065.756s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 d8 84 12 fc ff 7f ff ff ................
74 65 73 74 52 65 67 4b 72 65 74 70 72 6f 62 65 testRegKretprobe
backtrace:
[<ffff8000002cd880>] create_object+0x1e0/0x3f0
[<ffff800000fa3d6c>] kmemleak_alloc+0x6c/0xf0
[<ffff8000002ac97c>] __kmalloc+0x23c/0x2e0
[<ffff8000001a6f2c>] register_kretprobe+0x12c/0x350

When call register_kretprobes(struct kretprobe **rps, int num) with the
same rps(num>=2).
The first time,call INIT_HLIST_HEAD() and kmalloc() to malloc memory for the
hash list,then save into rp->free_instances.
The second time,call INIT_HLIST_HEAD() and kmalloc() then create a new
hash list into rp->free_instances and lost the first rp->free_instances.
So add check to avoid it.

Reported-and-tested-by: kangwen <kangwen1@...wei.com>
Signed-off-by: Bixuan Cui <cuibixuan@...wei.com>
---
 kernel/kprobes.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 6301dae..f19f191 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1890,10 +1890,16 @@ EXPORT_SYMBOL_GPL(register_kretprobe);

 int register_kretprobes(struct kretprobe **rps, int num)
 {
-	int ret = 0, i;
+	int ret = 0, i, j;

 	if (num <= 0)
 		return -EINVAL;
+
+	for (i = 0; i < num-1; i++)
+		for (j = i+1; j < num; j++)
+			if (rps[i] == rps[j])
+				return -EINVAL;
+
 	for (i = 0; i < num; i++) {
 		ret = register_kretprobe(rps[i]);
 		if (ret < 0) {
--
2.6.2



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