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io_uring: fix potential use after free on fallback request free 

After __io_free_req() puts a ctx ref, it should be assumed that the ctx
may already be gone. However, it can be accessed when putting the
fallback req. Free the req first and then put the ctx.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2020-06-29 13:13:03 +03:00 committed by Jens Axboe
parent 8eb7e2d007
commit ecfc517774
1 changed files with 5 additions and 2 deletions
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7
fs/io_uring.c
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@ -1526,12 +1526,15 @@ static void io_dismantle_req(struct io_kiocb *req)
static void __io_free_req(struct io_kiocb *req)
{
struct io_ring_ctx *ctx;
io_dismantle_req(req);
percpu_ref_put(&req->ctx->refs);
ctx = req->ctx;
if (likely(!io_is_fallback_req(req)))
kmem_cache_free(req_cachep, req);
else
clear_bit_unlock(0, (unsigned long *) &req->ctx->fallback_req);
clear_bit_unlock(0, (unsigned long *) &ctx->fallback_req);
percpu_ref_put(&ctx->refs);
}
static bool io_link_cancel_timeout(struct io_kiocb *req)