Re: [PATCH v6 1/1] ns: add binfmt_misc to the user namespace
flat view
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Date: 2018-10-16 18:03:33
Also in:
linux-fsdevel, lkml
On 2018-10-10 18:14, Laurent Vivier wrote:
quoted hunk ↗ jump to hunk
+ /* create a new binfmt namespace + * if we are not in the first user namespace + * but the binfmt namespace is the first one + */ + if (READ_ONCE(ns->binfmt_ns) == NULL) { + struct binfmt_namespace *new_ns; + + new_ns = kmalloc(sizeof(struct binfmt_namespace), + GFP_KERNEL); + if (new_ns == NULL) + return -ENOMEM; + INIT_LIST_HEAD(&new_ns->entries); + new_ns->enabled = 1; + rwlock_init(&new_ns->entries_lock); + new_ns->bm_mnt = NULL; + new_ns->entry_count = 0; + /* ensure new_ns is completely initialized before sharing it */ + smp_wmb(); + WRITE_ONCE(ns->binfmt_ns, new_ns); + }
If ns->binfmt_ns can really change under us (given you use READ_ONCE), what prevents two instances of this code running at the same time, in which case one of them would leak its new_ns instance? Also, there doesn't seem to be any smp_rmb() buddy to that wmb(), I don't think that's implied by READ_ONCE() in binfmt_ns(). Rasmus