Re: [PATCH] io_uring: avoid page allocation warnings

[Jens Axboe <axboe@xxxxxxxxx>]

On 5/1/19 9:09 AM, Mark Rutland wrote:
> On Wed, May 01, 2019 at 06:41:43AM -0600, Jens Axboe wrote:
>> On 5/1/19 4:30 AM, Mark Rutland wrote:
>>> On Tue, Apr 30, 2019 at 12:11:59PM -0600, Jens Axboe wrote:
>>>> On 4/30/19 11:03 AM, Mark Rutland wrote:
>>>>> I've just had a go at that, but when using kvmalloc() with or without
>>>>> GFP_KERNEL_ACCOUNT I hit OOM and my system hangs within a few seconds with the
>>>>> syzkaller prog below:
>>>>>
>>>>> ----
>>>>> Syzkaller reproducer:
>>>>> # {Threaded:false Collide:false Repeat:false RepeatTimes:0 Procs:1 Sandbox: Fault:false FaultCall:-1 FaultNth:0 EnableTun:false EnableNetDev:false EnableNetReset:false EnableCgroups:false EnableBinfmtMisc:false EnableCloseFds:false UseTmpDir:false HandleSegv:false Repro:false Trace:false}
>>>>> r0 = io_uring_setup(0x378, &(0x7f00000000c0))
>>>>> sendmsg$SEG6_CMD_SET_TUNSRC(0xffffffffffffffff, &(0x7f0000000240)={&(0x7f0000000000)={0x10, 0x0, 0x0, 0x40000000}, 0xc, 0x0, 0x1, 0x0, 0x0, 0x10}, 0x800)
>>>>> io_uring_register$IORING_REGISTER_BUFFERS(r0, 0x0, &(0x7f0000000000), 0x1)
>>>>> ----
>>>>>
>>>>> ... I'm a bit worried that opens up a trivial DoS.
>>>>>
>>>>> Thoughts?
>>>>
>>>> Can you post the patch you used?
>>>
>>> Diff below.
>>
>> And the reproducer, that was never posted.
> 
> It was; the "Syzakller reproducer" above is the reproducer I used with
> syz-repro.
> 
> I've manually minimized that to C below. AFAICT, that hits a leak, which
> is what's triggering the OOM after the program is run a number of times
> with the previously posted kvmalloc patch.
> 
> Per /proc/meminfo, that memory isn't accounted anywhere.
> 
>> Patch looks fine to me. Note
>> that buffer registration is under the protection of RLIMIT_MEMLOCK.
>> That's usually very limited for non-root, as root you can of course
>> consume as much as you want and OOM the system.
> 
> Sure.
> 
> As above, it looks like there's a leak, regardless.

The leak is that we're not releasing imu->bvec in case of error. I fixed
a missing kfree -> kvfree as well in your patch, with this rolled up
version it works for me.


diff --git a/fs/io_uring.c b/fs/io_uring.c
index 18cecb6a0151..3e817d40fb96 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2443,7 +2443,7 @@ static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
 
 		if (ctx->account_mem)
 			io_unaccount_mem(ctx->user, imu->nr_bvecs);
-		kfree(imu->bvec);
+		kvfree(imu->bvec);
 		imu->nr_bvecs = 0;
 	}
 
@@ -2533,11 +2533,11 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 
 		ret = 0;
 		if (!pages || nr_pages > got_pages) {
-			kfree(vmas);
-			kfree(pages);
-			pages = kmalloc_array(nr_pages, sizeof(struct page *),
+			kvfree(vmas);
+			kvfree(pages);
+			pages = kvmalloc_array(nr_pages, sizeof(struct page *),
 						GFP_KERNEL);
-			vmas = kmalloc_array(nr_pages,
+			vmas = kvmalloc_array(nr_pages,
 					sizeof(struct vm_area_struct *),
 					GFP_KERNEL);
 			if (!pages || !vmas) {
@@ -2549,7 +2549,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 			got_pages = nr_pages;
 		}
 
-		imu->bvec = kmalloc_array(nr_pages, sizeof(struct bio_vec),
+		imu->bvec = kvmalloc_array(nr_pages, sizeof(struct bio_vec),
 						GFP_KERNEL);
 		ret = -ENOMEM;
 		if (!imu->bvec) {
@@ -2588,6 +2588,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 			}
 			if (ctx->account_mem)
 				io_unaccount_mem(ctx->user, nr_pages);
+			kvfree(imu->bvec);
 			goto err;
 		}
 
@@ -2610,12 +2611,12 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 
 		ctx->nr_user_bufs++;
 	}
-	kfree(pages);
-	kfree(vmas);
+	kvfree(pages);
+	kvfree(vmas);
 	return 0;
 err:
-	kfree(pages);
-	kfree(vmas);
+	kvfree(pages);
+	kvfree(vmas);
 	io_sqe_buffer_unregister(ctx);
 	return ret;
 }

-- 
Jens Axboe