From: Al Viro Date: Wed, 7 Mar 2012 05:16:35 +0000 (+0000) Subject: aio: fix io_setup/io_destroy race X-Git-Tag: v3.2.12~39 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=00a1b4bfdec249286c6ed902773dd8699ae070d7 aio: fix io_setup/io_destroy race commit 86b62a2cb4fc09037bbce2959d2992962396fd7f upstream. 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... Signed-off-by: Al Viro Acked-by: Benjamin LaHaise Reviewed-by: Jeff Moyer Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/aio.c b/fs/aio.c index 67e4b9047cc9..f6578cb22d00 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); }