6.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jens Axboe <axboe@xxxxxxxxx> commit f8024f1f36a30a082b0457d5779c8847cea57f57 upstream. syzbot reports that registering a mapped buffer ring on arm32 can trigger an OOPS. Registered buffer rings have two modes, one of them is the application passing in the memory that the buffer ring should reside in. Once those pages are mapped, we use page_address() to get a virtual address. This will obviously fail on highmem pages, which aren't mapped. Add a check if we have any highmem pages after mapping, and fail the attempt to register a provided buffer ring if we do. This will return the same error as kernels that don't support provided buffer rings to begin with. Link: https://lore.kernel.org/io-uring/000000000000af635c0606bcb889@xxxxxxxxxx/ Fixes: c56e022c0a27 ("io_uring: add support for user mapped provided buffer ring") Cc: stable@xxxxxxxxxxxxxxx Reported-by: syzbot+2113e61b8848fa7951d8@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- io_uring/kbuf.c | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) --- a/io_uring/kbuf.c +++ b/io_uring/kbuf.c @@ -481,7 +481,7 @@ static int io_pin_pbuf_ring(struct io_ur { struct io_uring_buf_ring *br; struct page **pages; - int nr_pages; + int i, nr_pages; pages = io_pin_pages(reg->ring_addr, flex_array_size(br, bufs, reg->ring_entries), @@ -489,6 +489,17 @@ static int io_pin_pbuf_ring(struct io_ur if (IS_ERR(pages)) return PTR_ERR(pages); + /* + * Apparently some 32-bit boxes (ARM) will return highmem pages, + * which then need to be mapped. We could support that, but it'd + * complicate the code and slowdown the common cases quite a bit. + * So just error out, returning -EINVAL just like we did on kernels + * that didn't support mapped buffer rings. + */ + for (i = 0; i < nr_pages; i++) + if (PageHighMem(pages[i])) + goto error_unpin; + br = page_address(pages[0]); #ifdef SHM_COLOUR /* @@ -500,13 +511,8 @@ static int io_pin_pbuf_ring(struct io_ur * should use IOU_PBUF_RING_MMAP instead, and liburing will handle * this transparently. */ - if ((reg->ring_addr | (unsigned long) br) & (SHM_COLOUR - 1)) { - int i; - - for (i = 0; i < nr_pages; i++) - unpin_user_page(pages[i]); - return -EINVAL; - } + if ((reg->ring_addr | (unsigned long) br) & (SHM_COLOUR - 1)) + goto error_unpin; #endif bl->buf_pages = pages; bl->buf_nr_pages = nr_pages; @@ -514,6 +520,11 @@ static int io_pin_pbuf_ring(struct io_ur bl->is_mapped = 1; bl->is_mmap = 0; return 0; +error_unpin: + for (i = 0; i < nr_pages; i++) + unpin_user_page(pages[i]); + kvfree(pages); + return -EINVAL; } static int io_alloc_pbuf_ring(struct io_uring_buf_reg *reg,
