Messages in this thread | | | From | Lai Jiangshan <> | Date | Fri, 9 Jul 2021 11:49:21 +0800 | Subject | Re: [PATCH] workqueue: fix UAF in pwq_unbound_release_workfn() |
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On Thu, Jul 8, 2021 at 5:28 PM Yang Yingliang <yangyingliang@huawei.com> wrote: > > I got a UAF report when doing fuzz test: > > [ 152.880091][ T8030] ================================================================== > [ 152.881240][ T8030] BUG: KASAN: use-after-free in pwq_unbound_release_workfn+0x50/0x190 > [ 152.882442][ T8030] Read of size 4 at addr ffff88810d31bd00 by task kworker/3:2/8030 > [ 152.883578][ T8030] > [ 152.883932][ T8030] CPU: 3 PID: 8030 Comm: kworker/3:2 Not tainted 5.13.0+ #249 > [ 152.885014][ T8030] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 > [ 152.886442][ T8030] Workqueue: events pwq_unbound_release_workfn > [ 152.887358][ T8030] Call Trace: > [ 152.887837][ T8030] dump_stack_lvl+0x75/0x9b > [ 152.888525][ T8030] ? pwq_unbound_release_workfn+0x50/0x190 > [ 152.889371][ T8030] print_address_description.constprop.10+0x48/0x70 > [ 152.890326][ T8030] ? pwq_unbound_release_workfn+0x50/0x190 > [ 152.891163][ T8030] ? pwq_unbound_release_workfn+0x50/0x190 > [ 152.891999][ T8030] kasan_report.cold.15+0x82/0xdb > [ 152.892740][ T8030] ? pwq_unbound_release_workfn+0x50/0x190 > [ 152.893594][ T8030] __asan_load4+0x69/0x90 > [ 152.894243][ T8030] pwq_unbound_release_workfn+0x50/0x190 > [ 152.895057][ T8030] process_one_work+0x47b/0x890 > [ 152.895778][ T8030] worker_thread+0x5c/0x790 > [ 152.896439][ T8030] ? process_one_work+0x890/0x890 > [ 152.897163][ T8030] kthread+0x223/0x250 > [ 152.897747][ T8030] ? set_kthread_struct+0xb0/0xb0 > [ 152.898471][ T8030] ret_from_fork+0x1f/0x30 > [ 152.899114][ T8030] > [ 152.899446][ T8030] Allocated by task 8884: > [ 152.900084][ T8030] kasan_save_stack+0x21/0x50 > [ 152.900769][ T8030] __kasan_kmalloc+0x88/0xb0 > [ 152.901416][ T8030] __kmalloc+0x29c/0x460 > [ 152.902014][ T8030] alloc_workqueue+0x111/0x8e0 > [ 152.902690][ T8030] __btrfs_alloc_workqueue+0x11e/0x2a0 > [ 152.903459][ T8030] btrfs_alloc_workqueue+0x6d/0x1d0 > [ 152.904198][ T8030] scrub_workers_get+0x1e8/0x490 > [ 152.904929][ T8030] btrfs_scrub_dev+0x1b9/0x9c0 > [ 152.905599][ T8030] btrfs_ioctl+0x122c/0x4e50 > [ 152.906247][ T8030] __x64_sys_ioctl+0x137/0x190 > [ 152.906916][ T8030] do_syscall_64+0x34/0xb0 > [ 152.907535][ T8030] entry_SYSCALL_64_after_hwframe+0x44/0xae > [ 152.908365][ T8030] > [ 152.908688][ T8030] Freed by task 8884: > [ 152.909243][ T8030] kasan_save_stack+0x21/0x50 > [ 152.909893][ T8030] kasan_set_track+0x20/0x30 > [ 152.910541][ T8030] kasan_set_free_info+0x24/0x40 > [ 152.911265][ T8030] __kasan_slab_free+0xf7/0x140 > [ 152.911964][ T8030] kfree+0x9e/0x3d0 > [ 152.912501][ T8030] alloc_workqueue+0x7d7/0x8e0 > [ 152.913182][ T8030] __btrfs_alloc_workqueue+0x11e/0x2a0 > [ 152.913949][ T8030] btrfs_alloc_workqueue+0x6d/0x1d0 > [ 152.914703][ T8030] scrub_workers_get+0x1e8/0x490 > [ 152.915402][ T8030] btrfs_scrub_dev+0x1b9/0x9c0 > [ 152.916077][ T8030] btrfs_ioctl+0x122c/0x4e50 > [ 152.916729][ T8030] __x64_sys_ioctl+0x137/0x190 > [ 152.917414][ T8030] do_syscall_64+0x34/0xb0 > [ 152.918034][ T8030] entry_SYSCALL_64_after_hwframe+0x44/0xae > [ 152.918872][ T8030] > [ 152.919203][ T8030] The buggy address belongs to the object at ffff88810d31bc00 > [ 152.919203][ T8030] which belongs to the cache kmalloc-512 of size 512 > [ 152.921155][ T8030] The buggy address is located 256 bytes inside of > [ 152.921155][ T8030] 512-byte region [ffff88810d31bc00, ffff88810d31be00) > [ 152.922993][ T8030] The buggy address belongs to the page: > [ 152.923800][ T8030] page:ffffea000434c600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10d318 > [ 152.925249][ T8030] head:ffffea000434c600 order:2 compound_mapcount:0 compound_pincount:0 > [ 152.926399][ T8030] flags: 0x57ff00000010200(slab|head|node=1|zone=2|lastcpupid=0x7ff) > [ 152.927515][ T8030] raw: 057ff00000010200 dead000000000100 dead000000000122 ffff888009c42c80 > [ 152.928716][ T8030] raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000 > [ 152.929890][ T8030] page dumped because: kasan: bad access detected > [ 152.930759][ T8030] > [ 152.931076][ T8030] Memory state around the buggy address: > [ 152.931851][ T8030] ffff88810d31bc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > [ 152.932967][ T8030] ffff88810d31bc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > [ 152.934068][ T8030] >ffff88810d31bd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > [ 152.935189][ T8030] ^ > [ 152.935763][ T8030] ffff88810d31bd80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > [ 152.936847][ T8030] ffff88810d31be00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > [ 152.937940][ T8030] ================================================================== > > If apply_wqattrs_prepare() fails in alloc_workqueue(), it will call put_pwq() > which invoke a work queue to call pwq_unbound_release_workfn() and use the 'wq'. > The 'wq' allocated in alloc_workqueue() will be freed in error path when > apply_wqattrs_prepare() fails. So it will lead a UAF. > > CPU0 CPU1 > alloc_workqueue() > alloc_and_link_pwqs() > apply_wqattrs_prepare() fails > apply_wqattrs_cleanup() > schedule_work(&pwq->unbound_release_work) > kfree(wq) > worker_thread() > pwq_unbound_release_workfn() <- trigger uaf here > > In the error path of alloc_workqueue(), the variables will be freed, we > don't need the worker to free them, so just free the 'ctx' and its members > in the error path in apply_wqattrs_prepare(). > > Fixes: 2d5f0764b526 ("workqueue: split apply_workqueue_attrs() into 3 stages") > Reported-by: Hulk Robot <hulkci@huawei.com> > Co-developed-by: Xu Qiang <xuqiang36@huawei.com> > Signed-off-by: Xu Qiang <xuqiang36@huawei.com> > Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Thanks for the report and the fix.
> --- > kernel/workqueue.c | 27 ++++++++++++++++++++++++++- > 1 file changed, 26 insertions(+), 1 deletion(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 50142fc08902..1e71524fab31 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -3898,6 +3898,31 @@ struct apply_wqattrs_ctx { > struct pool_workqueue *pwq_tbl[]; > }; > > +static void free_pwq(struct pool_workqueue *pwq) > +{ > + if (!pwq || --pwq->refcnt) > + return; > + > + put_unbound_pool(pwq->pool); > + kmem_cache_free(pwq_cache, pwq); > +} > + > +static void free_wqattrs_ctx(struct apply_wqattrs_ctx *ctx) > +{ > + int node; > + > + if (!ctx) > + return; > + > + for_each_node(node) > + free_pwq(ctx->pwq_tbl[node]); > + free_pwq(ctx->dfl_pwq); > + > + free_workqueue_attrs(ctx->attrs); > + > + kfree(ctx); > +} > + > /* free the resources after success or abort */ > static void apply_wqattrs_cleanup(struct apply_wqattrs_ctx *ctx) > { > @@ -3981,7 +4006,7 @@ apply_wqattrs_prepare(struct workqueue_struct *wq, > out_free: > free_workqueue_attrs(tmp_attrs); > free_workqueue_attrs(new_attrs); > - apply_wqattrs_cleanup(ctx); > + free_wqattrs_ctx(ctx); > return NULL; > } >
For workqueue_apply_unbound_cpumask(), there will be the same problem because the new pwqs are not yet linked(link_pwq()) to the wq.
Please also add this to your patch.
@@ -5313,9 +5309,12 @@ static int workqueue_apply_unbound_cpumask(void) }
list_for_each_entry_safe(ctx, n, &ctxs, list) { - if (!ret) + if (!ret) { apply_wqattrs_commit(ctx); - apply_wqattrs_cleanup(ctx); + apply_wqattrs_cleanup(ctx); + } else { + free_wqattrs_ctx(ctx); + } }
return ret;
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