[PATCH] fsverity: explicitly check that there is no algorithm 0

[PATCH] fsverity: explicitly check that there is no algorithm 0

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Since libfsverity and some other code would break if 0 is ever allocated
as an FS_VERITY_HASH_ALG_* value, make fsverity_check_hash_algs()
explicitly check that there is no algorithm 0.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/verity/hash_algs.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c
index c598d20354763..6b08b1d9a7d7c 100644
--- a/fs/verity/hash_algs.c
+++ b/fs/verity/hash_algs.c
@@ -226,6 +226,14 @@ void __init fsverity_check_hash_algs(void)
 		if (!alg->name)
 			continue;
 
+		/*
+		 * 0 must never be allocated as an FS_VERITY_HASH_ALG_* value,
+		 * as it is reserved for users that use 0 to mean unspecified or
+		 * a default value.  fs/verity/ itself doesn't care and doesn't
+		 * have a default algorithm, but some users make use of this.
+		 */
+		BUG_ON(i == 0);
+
 		BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
 
 		/*

base-commit: ace1ba1c9038b30f29c5759bc4726bbed7748f15
-- 
2.41.0