Re: [PATCH] block, bfq: fix uaf for bfqq in bic_set_bfqq()

Hi,

在 2023/02/21 18:19, Holger Hoffstätte 写道:

On 2023-02-21 08:04, Yu Kuai wrote:

quoted

Hi, Jens

在 2023/01/13 17:44, Yu Kuai 写道:

quoted

After commit 64dc8c732f5c ("block, bfq: fix possible uaf for 
'bfqq->bic'"),
bic->bfqq will be accessed in bic_set_bfqq(), however, in some context
bic->bfqq will be freed first, and bic_set_bfqq() is called with the 
freed
bic->bfqq.

Fix the problem by always freeing bfqq after bic_set_bfqq().

Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
Reported-and-tested-by: Shinichiro Kawasaki 
[off-list ref]
Signed-off-by: Yu Kuai <redacted>
---
  block/bfq-cgroup.c  | 2 +-
  block/bfq-iosched.c | 4 +++-
  2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index a6e8da5f5cfd..feb13ac25557 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c

@@ -749,8 +749,8 @@ static void bfq_sync_bfqq_move(struct bfq_data 

*bfqd,
           * old cgroup.
           */
          bfq_put_cooperator(sync_bfqq);
-        bfq_release_process_ref(bfqd, sync_bfqq);
          bic_set_bfqq(bic, NULL, true, act_idx);
+        bfq_release_process_ref(bfqd, sync_bfqq);
      }
  }

It seems this change is missed in GIT PULL for-6.3. I'll send a seperate
patch to fix this...

It was already applied in time for 6.2 as 
b600de2d7d3a16f9007fad1bdae82a3951a26af2
and also already merged to 6.1-stable.

Yes, 6.2 and 6.1 doesn't have such problem because bfq_sync_bfqq_move()
doesn't exist. The problem only exist in master branch currently.

Thanks,
Kuai

cheers
Holger

.