Messages in this thread | | | Date | Fri, 4 Mar 2022 14:50:49 +0100 | From | David Sterba <> | Subject | Re: [PATCH] btrfs: don't access possibly stale fs_info data in device_list_add |
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On Fri, Mar 04, 2022 at 07:53:27AM +0800, Anand Jain wrote: > On 04/03/2022 02:24, David Sterba wrote: > > On Thu, Mar 03, 2022 at 10:40:27PM +0800, Dongliang Mu wrote: > >> > >> Fix this by modifying device->fs_info to NULL too. > >> > >> Reported-and-tested-by: syzbot+82650a4e0ed38f218363@syzkaller.appspotmail.com > >> Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com> > >> --- > >> fs/btrfs/volumes.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > >> index b07d382d53a8..c1325bdae9a1 100644 > >> --- a/fs/btrfs/volumes.c > >> +++ b/fs/btrfs/volumes.c > >> @@ -954,7 +954,7 @@ static noinline struct btrfs_device *device_list_add(const char *path, > >> task_pid_nr(current)); > >> return ERR_PTR(-EEXIST); > >> } > >> - btrfs_info_in_rcu(device->fs_info, > >> + btrfs_info_in_rcu(NULL, > > > > A few lines above this is also NULL and was fixed by 0697d9a61099 > > ("btrfs: don't access possibly stale fs_info data for printing duplicate > > device"), so yeah we probably need the same here. > > So it appears that device->fs_info was garbage instead of NULL OR > fs_info->sb was NULL?
I think it's a warning that something could happen, in this case potential garbage value of fs_info.
> Because we always had a check if fs_info is null in btrfs_printk() > further the commit a0f6d924cada ("btrfs: remove stub device info from > messages when we have no fs_info") made it better.
Yeah, that's removing a potential crash but still the NULL value could come from a freed memory. Seems taht we can't rely on fs_info in device_list_add at all and passing NULL is the only safe way.
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