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Subject[PATCH v2] block: bio_map_user_iov should not be limited to BIO_MAX_PAGES
Because bio_kmalloc uses inline iovecs, the limit on the number of entries
is not BIO_MAX_PAGES but rather UIO_MAXIOV, which indeed is already checked
in bio_kmalloc. This could cause SG_IO requests to be truncated and the HBA
to report a DMA overrun.

Note that if the argument to iov_iter_npages were changed to UIO_MAXIOV,
we would still truncate SG_IO requests beyond UIO_MAXIOV pages. Changing
it to UIO_MAXIOV + 1 instead ensures that bio_kmalloc notices that the
request is too big and blocks it.

Cc: Al Viro <>
Fixes: b282cc766958 ("bio_map_user_iov(): get rid of the iov_for_each()", 2017-10-11)
Signed-off-by: Paolo Bonzini <>

v1->v2: now with "git commit"
block/bio.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 4db1008309ed..0914ae4adae9 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1299,7 +1299,7 @@ struct bio *bio_map_user_iov(struct request_queue *q,
if (!iov_iter_count(iter))
return ERR_PTR(-EINVAL);

- bio = bio_kmalloc(gfp_mask, iov_iter_npages(iter, BIO_MAX_PAGES));
+ bio = bio_kmalloc(gfp_mask, iov_iter_npages(iter, UIO_MAXIOV + 1));
if (!bio)
return ERR_PTR(-ENOMEM);

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