[PATCHv2] io_uring: avoid page allocation warnings

From: Mark Rutland
Date: Wed May 01 2019 - 11:59:43 EST

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

Avoid this by using kvmalloc() for allocations dependent on the
user-provided iov_len. At the same time, fix a leak of imu->bvec when
registration fails.

Full splat from before this patch:

WARNING: CPU: 1 PID: 2314 at mm/page_alloc.c:4595 __alloc_pages_nodemask+0x7ac/0x2938 mm/page_alloc.c:4595
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 2314 Comm: syz-executor326 Not tainted 5.1.0-rc7-dirty #4
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0x0/0x2f0 include/linux/compiler.h:193
show_stack+0x20/0x30 arch/arm64/kernel/traps.c:158
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x110/0x190 lib/dump_stack.c:113
panic+0x384/0x68c kernel/panic.c:214
__warn+0x2bc/0x2c0 kernel/panic.c:571
report_bug+0x228/0x2d8 lib/bug.c:186
bug_handler+0xa0/0x1a0 arch/arm64/kernel/traps.c:956
call_break_hook arch/arm64/kernel/debug-monitors.c:301 [inline]
brk_handler+0x1d4/0x388 arch/arm64/kernel/debug-monitors.c:316
do_debug_exception+0x1a0/0x468 arch/arm64/mm/fault.c:831
__alloc_pages_nodemask+0x7ac/0x2938 mm/page_alloc.c:4595
alloc_pages_current+0x164/0x278 mm/mempolicy.c:2132
alloc_pages include/linux/gfp.h:509 [inline]
kmalloc_order+0x20/0x50 mm/slab_common.c:1231
kmalloc_order_trace+0x30/0x2b0 mm/slab_common.c:1243
kmalloc_large include/linux/slab.h:480 [inline]
__kmalloc+0x3dc/0x4f0 mm/slub.c:3791
kmalloc_array include/linux/slab.h:670 [inline]
io_sqe_buffer_register fs/io_uring.c:2472 [inline]
__io_uring_register fs/io_uring.c:2962 [inline]
__do_sys_io_uring_register fs/io_uring.c:3008 [inline]
__se_sys_io_uring_register fs/io_uring.c:2990 [inline]
__arm64_sys_io_uring_register+0x9e0/0x1bc8 fs/io_uring.c:2990
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:47 [inline]
el0_svc_common.constprop.0+0x148/0x2e0 arch/arm64/kernel/syscall.c:83
el0_svc_handler+0xdc/0x100 arch/arm64/kernel/syscall.c:129
el0_svc+0x8/0xc arch/arm64/kernel/entry.S:948
SMP: stopping secondary CPUs
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
CPU features: 0x002,23000438
Memory Limit: none
Rebooting in 1 seconds..

Fixes: edafccee56ff3167 ("io_uring: add support for pre-mapped user IO buffers")
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-block@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
fs/io_uring.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

Since v1:
* Use kvmalloc/kvfree
* Free imu->bvec in case of error (per Jens)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 578b5494f9e5..c6a22c2ae58f 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) {
- pages = kmalloc_array(nr_pages, sizeof(struct page *),
+ pages = kvmalloc_array(nr_pages, sizeof(struct page *),
- vmas = kmalloc_array(nr_pages,
+ vmas = kvmalloc_array(nr_pages,
sizeof(struct vm_area_struct *),
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),
ret = -ENOMEM;
if (!imu->bvec) {
@@ -2509,6 +2509,7 @@ 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;

@@ -2531,12 +2532,12 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,

- kfree(pages);
- kfree(vmas);
+ kvfree(pages);
+ kvfree(vmas);
return 0;
- kfree(pages);
- kfree(vmas);
+ kvfree(pages);
+ kvfree(vmas);
return ret;