| Message ID | 1458043730-14296-1-git-send-email-ptikhomirov@virtuozzo.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On Tue, Mar 15, 2016 at 03:08:50PM +0300, Pavel Tikhomirov wrote: > We probably need to fix superblock leak in patch (v4 "fs: Add user > namesapace member to struct super_block"): > > Imagine posible code path in sget_userns: we iterate through > type->fs_supers and do not find suitable sb, we drop sb_lock to > allocate s and go to retry. After we dropped sb_lock some other > task from different userns takes sb_lock, it is already in retry > stage and has s allocated, so it puts its s in type->fs_supers > list. So in retry we will find these sb in list and check it has > a different userns, and finally we will return without freeing s. > > Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com> Good catch. Acked-by: Seth Forshee <seth.forshee@canonical.com>
diff --git a/fs/super.c b/fs/super.c index b4ee02b..24771b5 100644 --- a/fs/super.c +++ b/fs/super.c @@ -458,6 +458,10 @@ struct super_block *sget_userns(struct file_system_type *type, continue; if (user_ns != old->s_user_ns) { spin_unlock(&sb_lock); + if (s) { + up_write(&s->s_umount); + destroy_super(s); + } return ERR_PTR(-EBUSY); } if (!grab_super(old))
We probably need to fix superblock leak in patch (v4 "fs: Add user namesapace member to struct super_block"): Imagine posible code path in sget_userns: we iterate through type->fs_supers and do not find suitable sb, we drop sb_lock to allocate s and go to retry. After we dropped sb_lock some other task from different userns takes sb_lock, it is already in retry stage and has s allocated, so it puts its s in type->fs_supers list. So in retry we will find these sb in list and check it has a different userns, and finally we will return without freeing s. Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com> --- fs/super.c | 4 ++++ 1 file changed, 4 insertions(+)