From 8105fbe6f19242cbf2168942dedc92bd708c4e2f Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Thu, 16 Apr 2026 07:02:46 +0800 Subject: [PATCH] ublk: use unchecked copy helpers for bio page data MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Bio pages may originate from slab caches that lack a usercopy region (e.g. jbd2 frozen metadata buffers allocated via jbd2_alloc()). When CONFIG_HARDENED_USERCOPY is enabled, copy_to_iter() calls check_copy_size() which rejects these slab pages, triggering a kernel BUG in usercopy_abort(). This is a false positive: the data is ordinary block I/O content — the same data the loop driver writes to its backing file via vfs_iter_write(). The bvec length is always trusted, so the size check in check_copy_size() is not needed either. Switch to _copy_to_iter()/_copy_from_iter() which skip the check_copy_size() wrapper while the underlying copy_to_user() remains unchanged. Acked-by: Caleb Sander Mateos Fixes: 2299ceec364e ("ublk: use copy_{to,from}_iter() for user copy") Signed-off-by: Ming Lei --- drivers/block/ublk_drv.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 603a98a30989..ef8a0705e68b 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -1319,10 +1319,18 @@ static bool ublk_copy_user_bvec(const struct bio_vec *bv, unsigned *offset, len = bv->bv_len - *offset; bv_buf = kmap_local_page(bv->bv_page) + bv->bv_offset + *offset; + /* + * Bio pages may originate from slab caches without a usercopy region + * (e.g. jbd2 frozen metadata buffers). This is the same data that + * the loop driver writes to its backing file — no exposure risk. + * The bvec length is always trusted, so the size check in + * check_copy_size() is not needed either. Use the unchecked + * helpers to avoid false positives on slab pages. + */ if (dir == ITER_DEST) - copied = copy_to_iter(bv_buf, len, uiter); + copied = _copy_to_iter(bv_buf, len, uiter); else - copied = copy_from_iter(bv_buf, len, uiter); + copied = _copy_from_iter(bv_buf, len, uiter); kunmap_local(bv_buf);