io_uring: prevent re-read of sqe->opcode
Liu reports that he can trigger a NULL pointer dereference with IORING_OP_SENDMSG, by changing the sqe->opcode after we've validated that the previous opcode didn't need a file and didn't assign one. Ensure we validate and read the opcode only once. Reported-by: Liu Yong <pkfxxxing@gmail.com> Tested-by: Liu Yong <pkfxxxing@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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