linux-kernel - [PATCH v4 1/3] aio_ring_remap: kill the bogus ctx->dead check

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Message-ID: <20150618184016.GA13488@redhat.com>
Date:	Thu, 18 Jun 2015 20:40:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-aio@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 1/3] aio_ring_remap: kill the bogus ctx->dead check

kill_ioctx() sets ctx->dead and removes ctx from ->ioctx_table
"atomically" under mm->ioctx_lock, so aio_ring_remap() can never
see a dead ctx.

And even -EINVAL doesn't look necessary. Yes, if mremap() races
with kill_ioctx() vm_munmap(ctx->mmap_base, ctx->mmap_size) can
unmap the wrong region. In this case the buggy application should
blame itself. And there are other reasons why that vm_munmap() can
be wrong. Say, an application can mremap() the part of aio region
and then do io_destroy(). We could change aio_ring_remap() to
verify vma->that vma_end - vma->vma_start == ctx->mmap_size but
this won't help if the application does munmap() instead.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/aio.c |    9 +++------
 1 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 480440f..893d300 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -325,14 +325,11 @@ static int aio_ring_remap(struct file *file, struct vm_area_struct *vma)
 	rcu_read_lock();
 	table = rcu_dereference(mm->ioctx_table);
 	for (i = 0; i < table->nr; i++) {
-		struct kioctx *ctx;
+		struct kioctx *ctx = table->table[i];

-		ctx = table->table[i];
 		if (ctx && ctx->aio_ring_file == file) {
-			if (!atomic_read(&ctx->dead)) {
-				ctx->user_id = ctx->mmap_base = vma->vm_start;
-				res = 0;
-			}
+			ctx->user_id = ctx->mmap_base = vma->vm_start;
+			res = 0;
 			break;
 		}
 	}
-- 
1.5.5.1

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