aio: restore locking of ioctx list on removal

[Mateusz Guzik]

Commit 36f5588905c10a8c4568a210d601fe8c3c27e0f0
"aio: refcounting cleanup" resulted in ioctx_lock not being held
during ctx removal, leaving the list susceptible to corruptions.

In mainline kernel the issue went away as a side effect of
db446a08c23d5475e6b08c87acca79ebb20f283c "aio: convert the ioctx list to
table lookup v3".

Fix the problem by restoring appropriate locking.

Signed-off-by: Mateusz Guzik <mguzik@xxxxxxxxxx>
Reported-by: Eryu Guan <eguan@xxxxxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Kent Overstreet <kmo@xxxxxxxxxxxxx>
Cc: linux-aio@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Acked-by: Benjamin LaHaise <bcrl@xxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 fs/aio.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 9b5ca11..975a5d5 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -425,10 +425,12 @@ static void kill_ioctx_rcu(struct rcu_head *head)
  *	when the processes owning a context have all exited to encourage
  *	the rapid destruction of the kioctx.
  */
-static void kill_ioctx(struct kioctx *ctx)
+static void kill_ioctx(struct mm_struct *mm, struct kioctx *ctx)
 {
 	if (!atomic_xchg(&ctx->dead, 1)) {
+		spin_lock(&mm->ioctx_lock);
 		hlist_del_rcu(&ctx->list);
+		spin_unlock(&mm->ioctx_lock);

 		/*
 		 * It'd be more correct to do this in free_ioctx(), after all
@@ -496,7 +498,7 @@ void exit_aio(struct mm_struct *mm)
 		 */
 		ctx->mmap_size = 0;

-		kill_ioctx(ctx);
+		kill_ioctx(mm, ctx);
 	}
 }

@@ -854,7 +856,7 @@ SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp)
 	if (!IS_ERR(ioctx)) {
 		ret = put_user(ioctx->user_id, ctxp);
 		if (ret)
-			kill_ioctx(ioctx);
+			kill_ioctx(current->mm, ioctx);
 		put_ioctx(ioctx);
 	}

@@ -872,7 +874,7 @@ SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
 {
 	struct kioctx *ioctx = lookup_ioctx(ctx);
 	if (likely(NULL != ioctx)) {
-		kill_ioctx(ioctx);
+		kill_ioctx(current->mm, ioctx);
 		put_ioctx(ioctx);
 		return 0;
 	}
--
1.8.3.2

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