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block: Fix start and length check added to iov_iter_extract_bvecs()

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Commit 14b007e178 added an address check using iter_iov_addr() and a
length check using iter_iov_len() to iov_iter_extract_bvecs(), but these
cannot be used so and are unsafe in this circumstance as the functions have
hardwired assumptions about the iterator type.  They should only be used
with ITER_UBUF or ITER_IOVEC-type iterators; they shouldn't be used with
ITER_BVEC, ITER_KVEC, ITER_FOLIOQ, ITER_XARRAY or ITER_DISCARD iterators.

This proves to be a problem for cachefiles as an iterator of type
ITER_FOLIOQ is passed and iter_iov_addr() and iter_iov_len() both
malfunction because iter->__iov in iter_iov() is not pointing to an iovec
array.

Fix this by using iov_iter_alignment() instead.

Fixes: 14b007e178 ("block: validate user space vectors during extraction")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/1667275.1788941191@warthog.procyon.org.uk
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
cc: Hannes Reinecke <hare@kernel.org>
cc: Christoph Hellwig <hch@infradead.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Paulo Alcantara <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
David Howells 2026-09-09 09:06:31 +01:00 • committed by Christian Brauner
commit 57a78ad230
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1 changed files with 16 additions and 2 deletions
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