[PATCH v4] block: bio-integrity: Fix null-ptr-deref in bio_integrity_map_user()

[Sungwoo Kim <iam@sung-woo.kim>]

pin_user_pages_fast() can partially succeed and return the number of
pages that were actually pinned. However, the bio_integrity_map_user()
does not handle this partial pinning. This leads to a general protection
fault since bvec_from_pages() dereferences an unpinned page address,
which is 0.

To fix this, add a check to verify that all requested memory is pinned.
If partial pinning occurs, unpin the memory and return -EFAULT.

Reproducer in blktest: https://github.com/linux-blktests/blktests/pull/244

Kernel Oops:

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 UID: 0 PID: 1061 Comm: nvme-passthroug Not tainted 7.0.0-11783-g90957f9314e8-dirty #16 PREEMPT(lazy)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
RIP: 0010:bio_integrity_map_user.cold+0x1b0/0x9d6

Fixes: 492c5d455969 ("block: bio-integrity: directly map user buffers")
Acked-by: Chao Shi <cshi008@fiu.edu>
Acked-by: Weidong Zhu <weizhu@fiu.edu>
Acked-by: Dave Tian <daveti@purdue.edu>
Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
---
V3: https://lore.kernel.org/linux-block/20260420020327.1667156-3-iam@sung-woo.kim/

V3->V4
- Addressed a sashiko's comments [1], if it makes sense.
- V3 wrongly assumed that iov_iter_extract_pages() always pins user
  memory.
- V3 insufficiently handled the return value range.

[1] https://sashiko.dev/#/patchset/20260420020327.1667156-3-iam%40sung-woo.kim

 block/bio-integrity.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/block/bio-integrity.c b/block/bio-integrity.c
index e54c6e06e1cb..766cc2d1d51c 100644
--- a/block/bio-integrity.c
+++ b/block/bio-integrity.c
@@ -403,6 +403,23 @@ int bio_integrity_map_user(struct bio *bio, struct iov_iter *iter)
 	if (unlikely(ret < 0))
 		goto free_bvec;
 
+	/* Handle partial pinning. This can happen when pin_user_pages_fast()
+	 * returns fewer pages than requested
+	 */
+	if (user_backed_iter(iter) && unlikely(ret != bytes)) {
+		if (0 < ret) {
+			int npinned = DIV_ROUND_UP(offset + ret, PAGE_SIZE);
+			int i;
+
+			for (i = 0; i < npinned; i++)
+				unpin_user_page(pages[i]);
+		}
+		if (pages != stack_pages)
+				kvfree(pages);
+		ret = -EFAULT;
+		goto free_bvec;
+	}
+
 	nr_bvecs = bvec_from_pages(bvec, pages, nr_vecs, bytes, offset,
 				   &is_p2p);
 	if (pages != stack_pages)
-- 
2.47.3