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From:   Matthias Kaehlcke <mka@chromium.org>
To:     Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>,
        Kees Cook <keescook@chromium.org>
Cc:     linux-security-module@vger.kernel.org, dm-devel@redhat.com,
        Douglas Anderson <dianders@chromium.org>,
        linux-kernel@vger.kernel.org,
        Sarthak Kukreti <sarthakkukreti@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>
Subject: [PATCH] dm: verity-loadpin: Only trust verity targets with enforcement
Date:   Wed,  7 Sep 2022 13:30:58 -0700
Message-Id: <20220907133055.1.Ic8a1dafe960dc0f8302e189642bc88ebb785d274@changeid>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Verity targets can be configured to ignore corrupted data blocks.
LoadPin must only trust verity targets that are configured to
perform some kind of enforcement when data corruption is detected,
like returning an error, restarting the system or triggering a
panic.

Fixes: b6c1c5745ccc ("dm: Add verity helpers for LoadPin")
Reported-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---

 drivers/md/dm-verity-loadpin.c |  8 ++++++++
 drivers/md/dm-verity-target.c  | 16 ++++++++++++++++
 drivers/md/dm-verity.h         |  1 +
 3 files changed, 25 insertions(+)

diff --git a/drivers/md/dm-verity-loadpin.c b/drivers/md/dm-verity-loadpin.c
index 387ec43aef72..4f78cc55c251 100644
--- a/drivers/md/dm-verity-loadpin.c
+++ b/drivers/md/dm-verity-loadpin.c
@@ -14,6 +14,7 @@ LIST_HEAD(dm_verity_loadpin_trusted_root_digests);
 
 static bool is_trusted_verity_target(struct dm_target *ti)
 {
+	int verity_mode;
 	u8 *root_digest;
 	unsigned int digest_size;
 	struct dm_verity_loadpin_trusted_root_digest *trd;
@@ -22,6 +23,13 @@ static bool is_trusted_verity_target(struct dm_target *ti)
 	if (!dm_is_verity_target(ti))
 		return false;
 
+	verity_mode = dm_verity_get_mode(ti);
+
+	if ((verity_mode != DM_VERITY_MODE_EIO) &&
+	    (verity_mode != DM_VERITY_MODE_RESTART) &&
+	    (verity_mode != DM_VERITY_MODE_PANIC))
+		return false;
+
 	if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))
 		return false;
 
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 94b6cb599db4..8a00cc42e498 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -1446,6 +1446,22 @@ bool dm_is_verity_target(struct dm_target *ti)
 	return ti->type->module == THIS_MODULE;
 }
 
+/*
+ * Get the verity mode (error behavior) of a verity target.
+ *
+ * Returns the verity mode of the target, or -EINVAL if 'ti' is not a verity
+ * target.
+ */
+int dm_verity_get_mode(struct dm_target *ti)
+{
+	struct dm_verity *v = ti->private;
+
+	if (!dm_is_verity_target(ti))
+		return -EINVAL;
+
+	return v->mode;
+}
+
 /*
  * Get the root digest of a verity target.
  *
diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index 45455de1b4bc..98f306ec6a33 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -134,6 +134,7 @@ extern int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,
 				 sector_t block, u8 *digest, bool *is_zero);
 
 extern bool dm_is_verity_target(struct dm_target *ti);
+extern int dm_verity_get_mode(struct dm_target *ti);
 extern int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest,
 				     unsigned int *digest_size);
 
-- 
2.37.2.789.g6183377224-goog