diff options
author | Robin Holt <holt@sgi.com> | 2013-02-23 00:35:34 (GMT) |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-02-28 13:38:31 (GMT) |
commit | d6f54cabb268370ccfb66e35a7ba9f0539987a13 (patch) | |
tree | 7fb2829bf53bc081f2b3db2cef22c6e6924386ec /mm | |
parent | 9b800caf48bac27baab53261e471d553f1f9809f (diff) | |
download | linux-fsl-qoriq-d6f54cabb268370ccfb66e35a7ba9f0539987a13.tar.xz |
mmu_notifier_unregister NULL Pointer deref and multiple ->release() callouts
commit 751efd8610d3d7d67b7bdf7f62646edea7365dd7 upstream.
There is a race condition between mmu_notifier_unregister() and
__mmu_notifier_release().
Assume two tasks, one calling mmu_notifier_unregister() as a result of a
filp_close() ->flush() callout (task A), and the other calling
mmu_notifier_release() from an mmput() (task B).
A B
t1 srcu_read_lock()
t2 if (!hlist_unhashed())
t3 srcu_read_unlock()
t4 srcu_read_lock()
t5 hlist_del_init_rcu()
t6 synchronize_srcu()
t7 srcu_read_unlock()
t8 hlist_del_rcu() <--- NULL pointer deref.
Additionally, the list traversal in __mmu_notifier_release() is not
protected by the by the mmu_notifier_mm->hlist_lock which can result in
callouts to the ->release() notifier from both mmu_notifier_unregister()
and __mmu_notifier_release().
-stable suggestions:
The stable trees prior to 3.7.y need commits 21a92735f660 and
70400303ce0c cherry-picked in that order prior to cherry-picking this
commit. The 3.7.y tree already has those two commits.
Signed-off-by: Robin Holt <holt@sgi.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Sagi Grimberg <sagig@mellanox.co.il>
Cc: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/mmu_notifier.c | 82 |
1 files changed, 42 insertions, 40 deletions
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index 8a5ac8c..f5c3d96 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -37,49 +37,51 @@ static struct srcu_struct srcu; void __mmu_notifier_release(struct mm_struct *mm) { struct mmu_notifier *mn; - struct hlist_node *n; int id; /* - * SRCU here will block mmu_notifier_unregister until - * ->release returns. + * srcu_read_lock() here will block synchronize_srcu() in + * mmu_notifier_unregister() until all registered + * ->release() callouts this function makes have + * returned. */ id = srcu_read_lock(&srcu); - hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) - /* - * if ->release runs before mmu_notifier_unregister it - * must be handled as it's the only way for the driver - * to flush all existing sptes and stop the driver - * from establishing any more sptes before all the - * pages in the mm are freed. - */ - if (mn->ops->release) - mn->ops->release(mn, mm); - srcu_read_unlock(&srcu, id); - spin_lock(&mm->mmu_notifier_mm->lock); while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) { mn = hlist_entry(mm->mmu_notifier_mm->list.first, struct mmu_notifier, hlist); + /* - * We arrived before mmu_notifier_unregister so - * mmu_notifier_unregister will do nothing other than - * to wait ->release to finish and - * mmu_notifier_unregister to return. + * Unlink. This will prevent mmu_notifier_unregister() + * from also making the ->release() callout. */ hlist_del_init_rcu(&mn->hlist); + spin_unlock(&mm->mmu_notifier_mm->lock); + + /* + * Clear sptes. (see 'release' description in mmu_notifier.h) + */ + if (mn->ops->release) + mn->ops->release(mn, mm); + + spin_lock(&mm->mmu_notifier_mm->lock); } spin_unlock(&mm->mmu_notifier_mm->lock); /* - * synchronize_srcu here prevents mmu_notifier_release to - * return to exit_mmap (which would proceed freeing all pages - * in the mm) until the ->release method returns, if it was - * invoked by mmu_notifier_unregister. - * - * The mmu_notifier_mm can't go away from under us because one - * mm_count is hold by exit_mmap. + * All callouts to ->release() which we have done are complete. + * Allow synchronize_srcu() in mmu_notifier_unregister() to complete + */ + srcu_read_unlock(&srcu, id); + + /* + * mmu_notifier_unregister() may have unlinked a notifier and may + * still be calling out to it. Additionally, other notifiers + * may have been active via vmtruncate() et. al. Block here + * to ensure that all notifier callouts for this mm have been + * completed and the sptes are really cleaned up before returning + * to exit_mmap(). */ synchronize_srcu(&srcu); } @@ -294,31 +296,31 @@ void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm) { BUG_ON(atomic_read(&mm->mm_count) <= 0); + spin_lock(&mm->mmu_notifier_mm->lock); if (!hlist_unhashed(&mn->hlist)) { - /* - * SRCU here will force exit_mmap to wait ->release to finish - * before freeing the pages. - */ int id; - id = srcu_read_lock(&srcu); /* - * exit_mmap will block in mmu_notifier_release to - * guarantee ->release is called before freeing the - * pages. + * Ensure we synchronize up with __mmu_notifier_release(). */ + id = srcu_read_lock(&srcu); + + hlist_del_rcu(&mn->hlist); + spin_unlock(&mm->mmu_notifier_mm->lock); + if (mn->ops->release) mn->ops->release(mn, mm); - srcu_read_unlock(&srcu, id); - spin_lock(&mm->mmu_notifier_mm->lock); - hlist_del_rcu(&mn->hlist); + /* + * Allow __mmu_notifier_release() to complete. + */ + srcu_read_unlock(&srcu, id); + } else spin_unlock(&mm->mmu_notifier_mm->lock); - } /* - * Wait any running method to finish, of course including - * ->release if it was run by mmu_notifier_relase instead of us. + * Wait for any running method to finish, including ->release() if it + * was run by __mmu_notifier_release() instead of us. */ synchronize_srcu(&srcu); |