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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	David Miller <davem@davemloft.net>,
	Jason Baron <jbaron@akamai.com>,
	kgraul@linux.ibm.com, ktkhai@virtuozzo.com,
	kyeongdon.kim@lge.com,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Netdev <netdev@vger.kernel.org>,
	pabeni@redhat.com, syzkaller-bugs@googlegroups.com,
	xiyou.wangcong@gmail.com, Christoph Hellwig <hch@lst.de>,
	zhengbin <zhengbin13@huawei.com>,
	bcrl@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-aio@kvack.org, houtao1@huawei.com, yi.zhang@huawei.com
Subject: [PATCH 1/8] pin iocb through aio.
Date: Sun, 10 Mar 2019 07:08:15 +0000	[thread overview]
Message-ID: <20190310070822.11564-1-viro@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20190310070606.GA10138@ZenIV.linux.org.uk>

From: Linus Torvalds <torvalds@linux-foundation.org>

aio_poll() is not the only case that needs file pinned; worse, while
aio_read()/aio_write() can live without pinning iocb itself, the
proof is rather brittle and can easily break on later changes.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/aio.c | 37 +++++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 3d9669d011b9..363d7d7c8bff 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1022,6 +1022,9 @@ static bool get_reqs_available(struct kioctx *ctx)
 /* aio_get_req
  *	Allocate a slot for an aio request.
  * Returns NULL if no requests are free.
+ *
+ * The refcount is initialized to 2 - one for the async op completion,
+ * one for the synchronous code that does this.
  */
 static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
 {
@@ -1034,7 +1037,7 @@ static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
 	percpu_ref_get(&ctx->reqs);
 	req->ki_ctx = ctx;
 	INIT_LIST_HEAD(&req->ki_list);
-	refcount_set(&req->ki_refcnt, 0);
+	refcount_set(&req->ki_refcnt, 2);
 	req->ki_eventfd = NULL;
 	return req;
 }
@@ -1067,15 +1070,18 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
 	return ret;
 }
 
+static inline void iocb_destroy(struct aio_kiocb *iocb)
+{
+	if (iocb->ki_filp)
+		fput(iocb->ki_filp);
+	percpu_ref_put(&iocb->ki_ctx->reqs);
+	kmem_cache_free(kiocb_cachep, iocb);
+}
+
 static inline void iocb_put(struct aio_kiocb *iocb)
 {
-	if (refcount_read(&iocb->ki_refcnt) == 0 ||
-	    refcount_dec_and_test(&iocb->ki_refcnt)) {
-		if (iocb->ki_filp)
-			fput(iocb->ki_filp);
-		percpu_ref_put(&iocb->ki_ctx->reqs);
-		kmem_cache_free(kiocb_cachep, iocb);
-	}
+	if (refcount_dec_and_test(&iocb->ki_refcnt))
+		iocb_destroy(iocb);
 }
 
 static void aio_fill_event(struct io_event *ev, struct aio_kiocb *iocb,
@@ -1749,9 +1755,6 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
 	INIT_LIST_HEAD(&req->wait.entry);
 	init_waitqueue_func_entry(&req->wait, aio_poll_wake);
 
-	/* one for removal from waitqueue, one for this function */
-	refcount_set(&aiocb->ki_refcnt, 2);
-
 	mask = vfs_poll(req->file, &apt.pt) & req->events;
 	if (unlikely(!req->head)) {
 		/* we did not manage to set up a waitqueue, done */
@@ -1782,7 +1785,6 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
 
 	if (mask)
 		aio_poll_complete(aiocb, mask);
-	iocb_put(aiocb);
 	return 0;
 }
 
@@ -1873,18 +1875,21 @@ static int __io_submit_one(struct kioctx *ctx, const struct iocb *iocb,
 		break;
 	}
 
+	/* Done with the synchronous reference */
+	iocb_put(req);
+
 	/*
 	 * If ret is 0, we'd either done aio_complete() ourselves or have
 	 * arranged for that to be done asynchronously.  Anything non-zero
 	 * means that we need to destroy req ourselves.
 	 */
-	if (ret)
-		goto out_put_req;
-	return 0;
+	if (!ret)
+		return 0;
+
 out_put_req:
 	if (req->ki_eventfd)
 		eventfd_ctx_put(req->ki_eventfd);
-	iocb_put(req);
+	iocb_destroy(req);
 out_put_reqs_available:
 	put_reqs_available(ctx, 1);
 	return ret;
-- 
2.11.0


  reply	other threads:[~2019-03-10  7:09 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-03 10:22 KASAN: use-after-free Read in unix_dgram_poll syzbot
2019-03-03 13:55 ` Al Viro
2019-03-03 15:18   ` [PATCH] aio: prevent the final fput() in the middle of vfs_poll() (Re: KASAN: use-after-free Read in unix_dgram_poll) Al Viro
2019-03-03 18:37     ` Eric Dumazet
2019-03-03 19:44     ` Linus Torvalds
2019-03-03 20:13       ` Linus Torvalds
2019-03-03 20:30       ` Al Viro
2019-03-03 22:23         ` Linus Torvalds
2019-03-04  2:36           ` Al Viro
2019-03-04 21:22             ` Linus Torvalds
2019-03-07  0:03               ` [PATCH 1/8] aio: make sure file is pinned Al Viro
2019-03-07  0:03                 ` [PATCH 2/8] aio_poll_wake(): don't set ->woken if we ignore the wakeup Al Viro
2019-03-07  2:18                   ` Al Viro
2019-03-08 11:16                     ` zhengbin (A)
2019-03-07  0:03                 ` [PATCH 3/8] aio_poll(): sanitize the logics after vfs_poll(), get rid of leak on error Al Viro
2019-03-07  2:11                   ` zhengbin (A)
2019-03-07  0:03                 ` [PATCH 4/8] aio_poll(): get rid of weird refcounting Al Viro
2019-03-07  0:03                 ` [PATCH 5/8] make aio_read()/aio_write() return int Al Viro
2019-03-07  0:03                 ` [PATCH 6/8] move dropping ->ki_eventfd into iocb_put() Al Viro
2019-03-07  0:03                 ` [PATCH 7/8] deal with get_reqs_available() in aio_get_req() itself Al Viro
2019-03-07  0:03                 ` [PATCH 8/8] aio: move sanity checks and request allocation to io_submit_one() Al Viro
2019-03-07  0:23                 ` [PATCH 1/8] aio: make sure file is pinned Linus Torvalds
2019-03-07  0:41                   ` Al Viro
2019-03-07  0:48                     ` Al Viro
2019-03-07  1:20                       ` Al Viro
2019-03-07  1:30                         ` Linus Torvalds
2019-03-08  3:36                           ` Al Viro
2019-03-08 15:50                             ` Christoph Hellwig
2019-03-10  7:06                             ` Al Viro
2019-03-10  7:08                               ` Al Viro [this message]
2019-03-10  7:08                                 ` [PATCH 2/8] keep io_event in aio_kiocb Al Viro
2019-03-11 19:43                                   ` Christoph Hellwig
2019-03-11 21:17                                     ` Al Viro
2019-03-10  7:08                                 ` [PATCH 3/8] aio: store event at final iocb_put() Al Viro
2019-03-11 19:44                                   ` Christoph Hellwig
2019-03-11 21:13                                     ` Al Viro
2019-03-11 22:52                                       ` Al Viro
2019-03-10  7:08                                 ` [PATCH 4/8] Fix aio_poll() races Al Viro
2019-03-11 19:58                                   ` Christoph Hellwig
2019-03-11 21:06                                     ` Al Viro
2019-03-12 19:18                                       ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 5/8] make aio_read()/aio_write() return int Al Viro
2019-03-11 19:44                                   ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 6/8] move dropping ->ki_eventfd into iocb_destroy() Al Viro
2019-03-11 19:46                                   ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 7/8] deal with get_reqs_available() in aio_get_req() itself Al Viro
2019-03-11 19:46                                   ` Christoph Hellwig
2019-03-10  7:08                                 ` [PATCH 8/8] aio: move sanity checks and request allocation to io_submit_one() Al Viro
2019-03-11 19:48                                   ` Christoph Hellwig
2019-03-11 21:12                                     ` Al Viro
2019-03-11 19:41                                 ` [PATCH 1/8] pin iocb through aio Christoph Hellwig
2019-03-11 19:41                               ` [PATCH 1/8] aio: make sure file is pinned Christoph Hellwig
2019-03-04  7:53     ` [PATCH] aio: prevent the final fput() in the middle of vfs_poll() (Re: KASAN: use-after-free Read in unix_dgram_poll) Dmitry Vyukov

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