Re: [PATCH] kernel/kprobes: add check to avoid memory leaks

[Bixuan Cui]

On 2017/10/25 20:29, Bixuan Cui wrote:
And test again with this patch:

insmod testRegKretprobes_004.ko
[  163.853281] register_kretprobe failed, returned -22
insmod: can't insert 'testRegKretprobes_004.ko': Operation not permitted

Thanks,
Bixuan Cui
> 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@xxxxxxxxxx>
> Signed-off-by: Bixuan Cui <cuibixuan@xxxxxxxxxx>
> ---
>  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
> 
> 
> 
> 
> .
>