[ upstream commit 05b538c1765f8d14a71ccf5f85258dcbeaf189f7 ]

We can look inside the fixed buffer table only while holding ->uring_lock, however in some cases we don't do the right async prep for IORING_OP_{WRITE,READ}_FIXED ending up with NULL req->imu forcing making an io-wq worker to try to resolve the fixed buffer without proper locking.

Move req->imu setup into early req init paths, i.e. io_prep_rw(), which is called unconditionally for rw requests and under uring_lock.

Fixes: 634d00df5e1cf ("io_uring: add full-fledged dynamic buffers support") Signed-off-by: Pavel Begunkov asml.silence@gmail.com --- fs/io_uring.c | 34 ++++++++++++++++++---------------- 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c index 68aab48838e4..fba15c42266c 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -3187,6 +3187,21 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe) int ret;

kiocb->ki_pos = READ_ONCE(sqe->off); + /* used for fixed read/write too - just read unconditionally */ + req->buf_index = READ_ONCE(sqe->buf_index); + req->imu = NULL; + + if (req->opcode == IORING_OP_READ_FIXED || + req->opcode == IORING_OP_WRITE_FIXED) { + struct io_ring_ctx *ctx = req->ctx; + u16 index; + + if (unlikely(req->buf_index >= ctx->nr_user_bufs)) + return -EFAULT; + index = array_index_nospec(req->buf_index, ctx->nr_user_bufs); + req->imu = ctx->user_bufs[index]; + io_req_set_rsrc_node(req, ctx, 0); + }

ioprio = READ_ONCE(sqe->ioprio); if (ioprio) { @@ -3199,11 +3214,9 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe) kiocb->ki_ioprio = get_current_ioprio(); }

- req->imu = NULL; req->rw.addr = READ_ONCE(sqe->addr); req->rw.len = READ_ONCE(sqe->len); req->rw.flags = READ_ONCE(sqe->rw_flags); - req->buf_index = READ_ONCE(sqe->buf_index); return 0; }

@@ -3335,20 +3348,9 @@ static int __io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter static int io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter, unsigned int issue_flags) { - struct io_mapped_ubuf *imu = req->imu; - u16 index, buf_index = req->buf_index; - - if (likely(!imu)) { - struct io_ring_ctx *ctx = req->ctx; - - if (unlikely(buf_index >= ctx->nr_user_bufs)) - return -EFAULT; - io_req_set_rsrc_node(req, ctx, issue_flags); - index = array_index_nospec(buf_index, ctx->nr_user_bufs); - imu = READ_ONCE(ctx->user_bufs[index]); - req->imu = imu; - } - return __io_import_fixed(req, rw, iter, imu); + if (WARN_ON_ONCE(!req->imu)) + return -EFAULT; + return __io_import_fixed(req, rw, iter, req->imu); }

static void io_ring_submit_unlock(struct io_ring_ctx *ctx, bool needs_lock)