From: Christian A. Ehrhardt Date: Sun, 21 Jan 2024 20:26:34 +0000 (+0100) Subject: block: Fix WARNING in _copy_from_iter X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=13f3956eb5681a4045a8dfdef48df5dc4d9f58a6;p=linux.git block: Fix WARNING in _copy_from_iter Syzkaller reports a warning in _copy_from_iter because an iov_iter is supposedly used in the wrong direction. The reason is that syzcaller managed to generate a request with a transfer direction of SG_DXFER_TO_FROM_DEV. This instructs the kernel to copy user buffers into the kernel, read into the copied buffers and then copy the data back to user space. Thus the iovec is used in both directions. Detect this situation in the block layer and construct a new iterator with the correct direction for the copy-in. Reported-by: syzbot+a532b03fdfee2c137666@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/0000000000009b92c10604d7a5e9@google.com/t/ Reported-by: syzbot+63dec323ac56c28e644f@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/0000000000003faaa105f6e7c658@google.com/T/ Signed-off-by: Christian A. Ehrhardt Reviewed-by: Christoph Hellwig Link: https://lore.kernel.org/r/20240121202634.275068-1-lk@c--e.de Signed-off-by: Jens Axboe --- diff --git a/block/blk-map.c b/block/blk-map.c index 8584babf3ea0c..71210cdb34426 100644 --- a/block/blk-map.c +++ b/block/blk-map.c @@ -205,12 +205,19 @@ static int bio_copy_user_iov(struct request *rq, struct rq_map_data *map_data, /* * success */ - if ((iov_iter_rw(iter) == WRITE && - (!map_data || !map_data->null_mapped)) || - (map_data && map_data->from_user)) { + if (iov_iter_rw(iter) == WRITE && + (!map_data || !map_data->null_mapped)) { ret = bio_copy_from_iter(bio, iter); if (ret) goto cleanup; + } else if (map_data && map_data->from_user) { + struct iov_iter iter2 = *iter; + + /* This is the copy-in part of SG_DXFER_TO_FROM_DEV. */ + iter2.data_source = ITER_SOURCE; + ret = bio_copy_from_iter(bio, &iter2); + if (ret) + goto cleanup; } else { if (bmd->is_our_pages) zero_fill_bio(bio);