On Tue, Apr 30, 2019 at 12:11:59PM -0600, Jens Axboe wrote:
> On 4/30/19 11:03 AM, Mark Rutland wrote:
> > On Tue, Apr 30, 2019 at 10:21:03AM -0600, Jens Axboe wrote:
> >> On 4/30/19 8:59 AM, Mark Rutland wrote:
> >>> On Tue, Apr 30, 2019 at 07:18:10AM -0700, Matthew Wilcox wrote:
> >>>> On Tue, Apr 30, 2019 at 02:24:05PM +0100, Mark Rutland wrote:
> >>>>> In io_sqe_buffer_register() we allocate a number of arrays based on the
> >>>>> iov_len from the user-provided iov. While we limit iov_len to SZ_1G,
> >>>>> we can still attempt to allocate arrays exceeding MAX_ORDER.
> >>>>>
> >>>>> On a 64-bit system with 4KiB pages, for an iov where iov_base = 0x10 and
> >>>>> iov_len = SZ_1G, we'll calculate that nr_pages = 262145. When we try to
> >>>>> allocate a corresponding array of (16-byte) bio_vecs, requiring 4194320
> >>>>> bytes, which is greater than 4MiB. This results in SLUB warning that
> >>>>> we're trying to allocate greater than MAX_ORDER, and failing the
> >>>>> allocation.
> >>>>>
> >>>>> Avoid this by passing __GFP_NOWARN when allocating arrays for the
> >>>>> user-provided iov_len. We'll gracefully handle the failed allocation,
> >>>>> returning -ENOMEM to userspace.
> >>>>>
> >>>>> We should probably consider lowering the limit below SZ_1G, or reworking
> >>>>> the array allocations.
> >>>>
> >>>> I'd suggest that kvmalloc is probably our friend here ... we don't really
> >>>> want to return -ENOMEM to userspace for this case, I don't think.
> >>>
> >>> Sure. I'll go verify that the uring code doesn't assume this memory is
> >>> physically contiguous.
> >>>
> >>> I also guess we should be passing GFP_KERNEL_ACCOUNT rateh than a plain
> >>> GFP_KERNEL.
> >>
> >> kvmalloc() is fine, the io_uring code doesn't care about the layout of
> >> the memory, it just uses it as an index.
> >
> > 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.
Mark.
---->8----
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 578b5494f9e5..c6dad90fab14 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2364,7 +2364,7 @@ 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;
}
@@ -2456,9 +2456,9 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
if (!pages || nr_pages > got_pages) {
kfree(vmas);
kfree(pages);
- pages = kmalloc_array(nr_pages, sizeof(struct page *),
+ 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) {
@@ -2470,7 +2470,7 @@ 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) {
@@ -2531,12 +2531,12 @@ 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;
}
--
2.11.0
