Both the read and write side use kiocb_done() to finish a request, and kiocb_done() will call io_put_kbuf() in case a provided buffer was used for the request. Provided buffers are not supported for writes, hence NULL is being passed in. This normally works fine, as io_put_kbuf() won't actually use the value unless REQ_F_BUFFER_RING or REQ_F_BUFFER_SELECTED is set in the request flags. But depending on compiler (or whether or not CONFIG_CC_OPTIMIZE_FOR_SIZE is set), that may be done even though the value is never used. This will then cause a NULL pointer dereference. Make it a bit more obvious and check for a NULL io_br_sel, and don't even bother calling io_put_kbuf() for that case. Fixes: 5fda51255439 ("io_uring/kbuf: switch to storing struct io_buffer_list locally") Reported-by: David Howells Tested-by: David Howells Signed-off-by: Jens Axboe --- diff --git a/io_uring/rw.c b/io_uring/rw.c index a0f9d2021e3f..5b2241a5813c 100644 --- a/io_uring/rw.c +++ b/io_uring/rw.c @@ -655,13 +655,17 @@ static int kiocb_done(struct io_kiocb *req, ssize_t ret, if (ret >= 0 && req->flags & REQ_F_CUR_POS) req->file->f_pos = rw->kiocb.ki_pos; if (ret >= 0 && !(req->ctx->flags & IORING_SETUP_IOPOLL)) { + u32 cflags = 0; + __io_complete_rw_common(req, ret); /* * Safe to call io_end from here as we're inline * from the submission path. */ io_req_io_end(req); - io_req_set_res(req, final_ret, io_put_kbuf(req, ret, sel->buf_list)); + if (sel) + cflags = io_put_kbuf(req, ret, sel->buf_list); + io_req_set_res(req, final_ret, cflags); io_req_rw_cleanup(req, issue_flags); return IOU_COMPLETE; } else { -- Jens Axboe