[PATCH 2/2] ipe: protect the dm-verity root hash with RCU

[Fan Wu]

ipe_bdev_setintegrity() frees the old root hash when dm-verity publishes
a new one on ->preresume, while policy evaluation can still be
dereferencing it.

Protect the root hash with RCU. The evaluation path already runs under
rcu_read_lock().

Fixes: e155858dd995 ("ipe: add support for dm-verity as a trust provider")
Cc: stable at vger.kernel.org
Assisted-by: claude-opus-5.5
Signed-off-by: Fan Wu <wufan at kernel.org>
---
 security/ipe/eval.c  | 12 ++++++++----
 security/ipe/eval.h  |  2 +-
 security/ipe/hooks.c | 22 +++++++++++++++++-----
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/security/ipe/eval.c b/security/ipe/eval.c
index 21439c5be336..4a7be96c84f0 100644
--- a/security/ipe/eval.c
+++ b/security/ipe/eval.c
@@ -134,10 +134,14 @@ static bool evaluate_boot_verified(const struct ipe_eval_ctx *const ctx)
 static bool evaluate_dmv_roothash(const struct ipe_eval_ctx *const ctx,
 				  struct ipe_prop *p)
 {
-	return !!ctx->ipe_bdev &&
-	       !!ctx->ipe_bdev->root_hash &&
-	       ipe_digest_eval(p->value,
-			       ctx->ipe_bdev->root_hash);
+	const struct digest_info *root_hash;
+
+	if (!ctx->ipe_bdev)
+		return false;
+
+	root_hash = rcu_dereference(ctx->ipe_bdev->root_hash);
+
+	return root_hash && ipe_digest_eval(p->value, root_hash);
 }
 #else
 static bool evaluate_dmv_roothash(const struct ipe_eval_ctx *const ctx,
diff --git a/security/ipe/eval.h b/security/ipe/eval.h
index fef65a36468c..b26d1147d070 100644
--- a/security/ipe/eval.h
+++ b/security/ipe/eval.h
@@ -27,7 +27,7 @@ struct ipe_bdev {
 #ifdef CONFIG_IPE_PROP_DM_VERITY_SIGNATURE
 	bool dm_verity_signed;
 #endif /* CONFIG_IPE_PROP_DM_VERITY_SIGNATURE */
-	struct digest_info *root_hash;
+	struct digest_info __rcu *root_hash;
 };
 #endif /* CONFIG_IPE_PROP_DM_VERITY */
 
diff --git a/security/ipe/hooks.c b/security/ipe/hooks.c
index 0ae54a880405..d878b52ceec8 100644
--- a/security/ipe/hooks.c
+++ b/security/ipe/hooks.c
@@ -9,6 +9,7 @@
 #include <linux/binfmts.h>
 #include <linux/mman.h>
 #include <linux/blk_types.h>
+#include <linux/rcupdate.h>
 
 #include "ipe.h"
 #include "hooks.h"
@@ -232,7 +233,20 @@ void ipe_bdev_free_security(struct block_device *bdev)
 {
 	struct ipe_bdev *blob = ipe_bdev(bdev);
 
-	ipe_digest_free(blob->root_hash);
+	ipe_digest_free(rcu_access_pointer(blob->root_hash));
+}
+
+static void ipe_set_dmverity_roothash(struct ipe_bdev *blob,
+				      struct digest_info *info)
+{
+	struct digest_info *old;
+
+	/* Protected by device-mapper's md->suspend_lock */
+	old = rcu_replace_pointer(blob->root_hash, info, true);
+	if (old) {
+		synchronize_rcu();
+		ipe_digest_free(old);
+	}
 }
 
 #ifdef CONFIG_IPE_PROP_DM_VERITY_SIGNATURE
@@ -280,8 +294,7 @@ int ipe_bdev_setintegrity(struct block_device *bdev, enum lsm_integrity_type typ
 		return -EINVAL;
 
 	if (!value) {
-		ipe_digest_free(blob->root_hash);
-		blob->root_hash = NULL;
+		ipe_set_dmverity_roothash(blob, NULL);
 
 		return 0;
 	}
@@ -301,8 +314,7 @@ int ipe_bdev_setintegrity(struct block_device *bdev, enum lsm_integrity_type typ
 
 	info->digest_len = digest->digest_len;
 
-	ipe_digest_free(blob->root_hash);
-	blob->root_hash = info;
+	ipe_set_dmverity_roothash(blob, info);
 
 	return 0;
 err:
-- 
2.55.0