From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: races in ipathfs Date: Thu, 19 Jan 2012 20:20:04 +0000 Message-ID: <20120119202003.GZ23916@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Mike Marciniszyn Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@vger.kernel.org Use of qib_super is seriously racy. qibfs_add() (and worse, qibfs_remove()) can happen during qibfs_mount() and qibfs_kill_super(). 1) CPU1: qib_init_one(). The sucker is allocated and placed on the list. CPU2: ipathfs is mounted, directory created. CPU1: finally gets around to qibfs_add(); by now qib_super is non-NULL and off we go, trying to create it again. The worst part is, that code doesn't even notice that dentry is there and positive; you silently leak the old inode. 2) CPU1: qib_init_one(). Allocated the sucker. CPU2: ipathfs is getting mounted. Picked the first device off the list, creating directory for it. CPU1: inserted new device into the head of the list, continued working. Got around to qibfs_add(); qib_super is NULL, so we do nothing. CPU2: walked the rest of the list, creating directories for all devices. Our device is missed, since we are past that point in the list. Worse, shift the timing a bit and it doesn't matter whether you add to the head or to the tail of the list - if qibfs_add() happens just before we set qib_super, we are screwed again. 3) CPU1: qib_remove_one(). CPU2: mount ipathfs is walking that list and decides to try and create a directory for the device that is being freed. Oops... 4) CPU1: qib_init_one() or qib_remove_one(), doesn't matter which. CPU2: final umount of ipathfs already got through setting sb->s_root to NULL but still hadn't set qib_super to the same. Oops... And no, moving that qib_super = NULL; up prior to kill_litter_super() won't fix the race either, of course. AFAICS, the older driver (in hw/ipath) has the same problems. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html