Messages in this thread | | | Subject | Re: [PATCH] block, bfq: fix possible uaf for 'bfqq->bic' | From | Yu Kuai <> | Date | Tue, 13 Dec 2022 18:32:20 +0800 |
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Hi, Jan!
在 2022/12/12 21:35, Jan Kara 写道: > On Sat 10-12-22 18:25:37, Yu Kuai wrote: >> From: Yu Kuai <yukuai3@huawei.com> >> >> Our test report a uaf for 'bfqq->bic' in 5.10: >> >> ================================================================== >> BUG: KASAN: use-after-free in bfq_select_queue+0x378/0xa30 >> Read of size 8 at addr ffff88810efb42d8 by task fsstress/2318352 >> >> CPU: 6 PID: 2318352 Comm: fsstress Kdump: loaded Not tainted 5.10.0-60.18.0.50.h602.kasan.eulerosv2r11.x86_64 #1 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-20220320_160524-szxrtosci10000 04/01/2014 >> Call Trace: > ... >> bfq_select_queue+0x378/0xa30 >> __bfq_dispatch_request+0x1c4/0x220 >> bfq_dispatch_request+0xe8/0x130 >> __blk_mq_do_dispatch_sched+0x3f4/0x560 >> blk_mq_do_dispatch_sched+0x62/0xb0 >> __blk_mq_sched_dispatch_requests+0x215/0x2a0 >> blk_mq_sched_dispatch_requests+0x8f/0xd0 >> __blk_mq_run_hw_queue+0x98/0x180 >> __blk_mq_delay_run_hw_queue+0x22b/0x240 >> blk_mq_run_hw_queue+0xe3/0x190 >> blk_mq_sched_insert_requests+0x107/0x200 >> blk_mq_flush_plug_list+0x26e/0x3c0 >> blk_finish_plug+0x63/0x90 >> __iomap_dio_rw+0x7b5/0x910 >> iomap_dio_rw+0x36/0x80 >> ext4_dio_read_iter+0x146/0x190 [ext4] >> ext4_file_read_iter+0x1e2/0x230 [ext4] >> new_sync_read+0x29f/0x400 >> vfs_read+0x24e/0x2d0 >> ksys_read+0xd5/0x1b0 > > Perhaps we can trim this UAF report a bit to what I've left above? That > should be enough to give idea about the problem. Yes, of course. > >> Commit 3bc5e683c67d ("bfq: Split shared queues on move between cgroups") >> changes that move process to a new cgroup will allocate a new bfqq to >> use, however, the old bfqq and new bfqq can point to the same bic: >> >> 1) Initial state, two process with io in the same cgroup. >> >> Process 1 Process 2 >> (BIC1) (BIC2) >> | Λ | Λ >> | | | | >> V | V | >> bfqq1 bfqq2 >> >> 2) bfqq1 is merged to bfqq2. >> >> Process 1 Process 2(cg1) >> (BIC1) (BIC2) >> | | >> \-------------\| >> V >> bfqq1 bfqq2(coop) >> >> 3) Process 1 exit, then issue new io(denoce IOA) from Process 2. >> >> (BIC2) >> | Λ >> | | >> V | >> bfqq2(coop) >> >> 4) Before IOA is completed, move Process 2 to another cgroup and issue io. >> >> Process 2 >> (BIC2) >> Λ >> |\--------------\ >> | V >> bfqq2 bfqq3 >> >> Now that BIC2 points to bfqq3, while bfqq2 and bfqq3 both point to BIC2. >> If all the requests are completed, and Process 2 exit, BIC2 will be >> freed while there is no guarantee that bfqq2 will be freed before BIC2. >> >> Fix the problem by clearing bfqq->bic if process references is decreased >> to zero, since that they are not related anymore. >> >> Fixes: 3bc5e683c67d ("bfq: Split shared queues on move between cgroups") >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> > > Thanks for the analysis and the patch! I agree this is a problem. > >> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >> index a72304c728fc..6eada99d1b34 100644 >> --- a/block/bfq-iosched.c >> +++ b/block/bfq-iosched.c >> @@ -3036,6 +3036,14 @@ void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq) >> >> bfq_reassign_last_bfqq(bfqq, NULL); >> >> + /* >> + * __bfq_bic_change_cgroup() just reset bic->bfqq so that a new bfqq >> + * will be created to handle new io, while old bfqq will stay around >> + * until all the requests are completed. It's unsafe to keep bfqq->bic >> + * since they are not related anymore. >> + */ >> + if (bfqq_process_refs(bfqq) == 1) >> + bfqq->bic = NULL; >> bfq_put_queue(bfqq); > > Rather than changing bfq_release_process_ref() I think it would be more > logical to change bic_set_bfqq() like: > > struct bfq_queue *old_bfqq = bic->bfqq[is_sync]; > > /* Clear bic pointer if we are detaching bfqq from its bic */ > if (old_bfqq && old_bfqq->bic == bic) > old_bfqq->bic = NULL; > > And then we can also remove several explicit bfqq->bic = NULL statements > from bfq code.
Yes, I agree. I'll send a new patch soon.
Thanks, Kuai > > Honza >
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