block: Allow bio_iov_iter_get_pages() with bio->bi_bdev unset

bio_iov_iter_get_pages() trims the IO based on the block size of the
block device the IO will be issued to.

However, bcachefs is a multi device filesystem; when we're creating the
bio we don't yet know which block device the bio will be submitted to -
we have to handle the alignment checks elsewhere.

Thus this is needed to avoid a null ptr deref.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Link: https://lore.kernel.org/r/20230813182636.2966159-3-kent.overstreet@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bio.c b/block/bio.c
index bb3ea4e05d4ca15a84ac54ace37661bc2e8151b0..be484d87142b8301a1cbb547167e44ad5960df8d 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -1231,7 +1231,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
        struct page **pages = (struct page **)bv;
        ssize_t size, left;
        unsigned len, i = 0;
-       size_t offset, trim;
+       size_t offset;
        int ret = 0;
 
        /*
@@ -1260,10 +1260,12 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 
        nr_pages = DIV_ROUND_UP(offset + size, PAGE_SIZE);
 
-       trim = size & (bdev_logical_block_size(bio->bi_bdev) - 1);
-       iov_iter_revert(iter, trim);
+       if (bio->bi_bdev) {
+               size_t trim = size & (bdev_logical_block_size(bio->bi_bdev) - 1);
+               iov_iter_revert(iter, trim);
+               size -= trim;
+       }
 
-       size -= trim;
        if (unlikely(!size)) {
                ret = -EFAULT;
                goto out;