CVE-2023-53511

In the Linux kernel, the following vulnerability has been resolved:

io_uring: fix fget leak when fs don't support nowait buffered read

Heming reported a BUG when using io_uring doing link-cp on ocfs2. [1]

Do the following steps can reproduce this BUG: mount -t ocfs2 /dev/vdc /mnt/ocfs2 cp testfile /mnt/ocfs2/ ./link-cp /mnt/ocfs2/testfile /mnt/ocfs2/testfile.1 umount /mnt/ocfs2

Then umount will fail, and it outputs: umount: /mnt/ocfs2: target is busy.

While tracing umount, it blames mntgetcount() not return as expected. Do a deep investigation for fget()/fput() on related code flow, I've finally found that fget() leaks since ocfs2 doesn't support nowait buffered read.

ioissuesqe |-ioassignfile // do fget() first |-ioread |-ioiterdoread |-ocfs2filereaditer // return -EOPNOTSUPP |-kiocbdone |-iorwdone |-_iocompleterwcommon // set REQFREISSUE |-ioresubmitprep |-ioreqprep_async // override req->file, leak happens

This was introduced by commit a196c78b5443 in v5.18. Fix it by don't re-assign req->file if it has already been assigned.

[1] https://lore.kernel.org/ocfs2-devel/ab580a75-91c8-d68a-3455-40361be1bfa8@linux.alibaba.com/T/#t