Messages in this thread Patch in this message |  | | | Date | Wed, 7 Mar 2012 05:16:35 +0000 | | From | Al Viro <> | | Subject | [PATCH] aio: fix io_setup/io_destroy race |
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Have ioctx_alloc() return an extra reference, so that caller would drop it on success and not bother with re-grabbing it on failure exit. The current code is obviously broken - io_destroy() from another thread that managed to guess the address io_setup() would've returned would free ioctx right under us; gets especially interesting if aio_context_t * we pass to io_setup() points to PROT_READ mapping, so put_user() fails and we end up doing io_destroy() on kioctx another thread has just got freed...
Cc: stable@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> --- [there's other pending aio stuff, but this part is really obvious and self-contained] diff --git a/fs/aio.c b/fs/aio.c index 67e4b90..f6578cb 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -273,7 +273,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) mm = ctx->mm = current->mm; atomic_inc(&mm->mm_count); - atomic_set(&ctx->users, 1); + atomic_set(&ctx->users, 2); spin_lock_init(&ctx->ctx_lock); spin_lock_init(&ctx->ring_info.ring_lock); init_waitqueue_head(&ctx->wait); @@ -1338,10 +1338,10 @@ SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp) ret = PTR_ERR(ioctx); if (!IS_ERR(ioctx)) { ret = put_user(ioctx->user_id, ctxp); - if (!ret) + if (!ret) { + put_ioctx(ioctx); return 0; - - get_ioctx(ioctx); /* io_destroy() expects us to hold a ref */ + } io_destroy(ioctx); }
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