2022-03-04 19:14:26

by Jeff Layton

Subject: Re: [PATCH 2/3] ceph: fix use-after-free in ceph_readdir

On Fri, 2022-03-04 at 16:14 +0000, Lu?s Henriques wrote:
> After calling ceph_mdsc_put_request() on dfi->last_readdir, this field
> should be set to NULL, otherwise we may end-up freeing it twince and get
> the following splat:
>
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 0 PID: 229 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
> ...
> Call Trace:
> <TASK>
> ceph_readdir+0xd35/0x1460 [ceph]
> ? _raw_spin_unlock+0x12/0x30
> ? preempt_count_add+0x73/0xa0
> ? _raw_spin_unlock+0x12/0x30
> ? __mark_inode_dirty+0x27c/0x3a0
> iterate_dir+0x7d/0x190
> __x64_sys_getdents64+0x80/0x120
> ? compat_fillonedir+0x160/0x160
> do_syscall_64+0x43/0x90
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Signed-off-by: Lu?s Henriques <[email protected]>
> ---
> fs/ceph/dir.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> index 0bcb677d2199..934402f5e9e6 100644
> --- a/fs/ceph/dir.c
> +++ b/fs/ceph/dir.c
> @@ -555,6 +555,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> le32_to_cpu(rde->inode.in->mode) >> 12)) {
> dout("filldir stopping us...\n");
> ceph_mdsc_put_request(dfi->last_readdir);
> + dfi->last_readdir = NULL;
> err = 0;
> goto out;
> }

I think Xiubo fixed this in the testing branch late yesterday. It should
no longer be needed.

Thanks,
--
Jeff Layton <[email protected]>

2022-03-05 16:11:14

by Xiubo Li

Subject: Re: [PATCH 2/3] ceph: fix use-after-free in ceph_readdir

On 3/5/22 2:20 AM, Jeff Layton wrote:
> On Fri, 2022-03-04 at 16:14 +0000, Lu?s Henriques wrote:
>> After calling ceph_mdsc_put_request() on dfi->last_readdir, this field
>> should be set to NULL, otherwise we may end-up freeing it twince and get
>> the following splat:
>>
>> refcount_t: underflow; use-after-free.
>> WARNING: CPU: 0 PID: 229 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
>> ...
>> Call Trace:
>> <TASK>
>> ceph_readdir+0xd35/0x1460 [ceph]
>> ? _raw_spin_unlock+0x12/0x30
>> ? preempt_count_add+0x73/0xa0
>> ? _raw_spin_unlock+0x12/0x30
>> ? __mark_inode_dirty+0x27c/0x3a0
>> iterate_dir+0x7d/0x190
>> __x64_sys_getdents64+0x80/0x120
>> ? compat_fillonedir+0x160/0x160
>> do_syscall_64+0x43/0x90
>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> Signed-off-by: Lu?s Henriques <[email protected]>
>> ---
>> fs/ceph/dir.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
>> index 0bcb677d2199..934402f5e9e6 100644
>> --- a/fs/ceph/dir.c
>> +++ b/fs/ceph/dir.c
>> @@ -555,6 +555,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
>> le32_to_cpu(rde->inode.in->mode) >> 12)) {
>> dout("filldir stopping us...\n");
>> ceph_mdsc_put_request(dfi->last_readdir);
>> + dfi->last_readdir = NULL;
>> err = 0;
>> goto out;
>> }
> I think Xiubo fixed this in the testing branch late yesterday. It should
> no longer be needed.

Right and I have sent a new version of my previous patch to remove the
buggy code.

- Xiubo

> Thanks,