linux-kernel - [PATCH v2 1/6] device-mapper: Check that target specs are sufficiently aligned

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Message-Id: <20230603145244.1538-2-demi@invisiblethingslab.com>
Date:   Sat,  3 Jun 2023 10:52:39 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com
Cc:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH v2 1/6] device-mapper: Check that target specs are sufficiently aligned

Otherwise subsequent code will dereference a misaligned
`struct dm_target_spec *`, which is undefined behavior.

Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
---
 drivers/md/dm-ioctl.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param)
 static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
 		       struct dm_target_spec **spec, char **target_params)
 {
+	static_assert(_Alignof(struct dm_target_spec) <= 8,
+		      "struct dm_target_spec has excessive alignment requirements");
+	if (next % 8) {
+		DMERR("Next target spec (offset %u) is not 8-byte aligned", next);
+		return -EINVAL;
+	}
+
 	*spec = (struct dm_target_spec *) ((unsigned char *) last + next);
 	*target_params = (char *) (*spec + 1);
 
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab