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

[Masami Hiramatsu]

On Mon, 30 Oct 2017 09:10:57 +0800
Bixuan Cui <cuibixuan@xxxxxxxxxx> wrote:

> 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.
> > 

I don't like this kind of check, since this is obviously caller's bug.
Why doesn't each caller check this?

Thank you,

> > 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
> > 
> > 
> > 
> > 
> > .
> > 
> 
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>