Handle and detect #13709's unlock regression (#14161)

In #13709, as in #11294 before it, it turns out that 63a26454 still had
the same failure mode as when it was first landed as d1d47691, and
fails to unlock certain datasets that formerly worked.

Rather than reverting it again, let's add handling to just throw out
the accounting metadata that failed to unlock when that happens, as
well as a test with a pre-broken pool image to ensure that we never get
bitten by this again.

Fixes: #13709

Signed-off-by: Rich Ercolani <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>

1 files changed, 19 insertions, 4 deletions

diff --git a/module/zfs/dsl_crypt.c b/module/zfs/dsl_crypt.c
index 1ea184de3..bf1f55e68 100644
--- a/module/zfs/dsl_crypt.c
+++ b/module/zfs/dsl_crypt.c
@@ -2672,6 +2672,7 @@ spa_do_crypt_objset_mac_abd(boolean_t generate, spa_t *spa, uint64_t dsobj,
 	objset_phys_t *osp = buf;
 	uint8_t portable_mac[ZIO_OBJSET_MAC_LEN];
 	uint8_t local_mac[ZIO_OBJSET_MAC_LEN];
+	const uint8_t zeroed_mac[ZIO_OBJSET_MAC_LEN] = {0};
 
 	/* look up the key from the spa's keystore */
 	ret = spa_keystore_lookup_key(spa, dsobj, FTAG, &dck);
@@ -2694,10 +2695,24 @@ spa_do_crypt_objset_mac_abd(boolean_t generate, spa_t *spa, uint64_t dsobj,
 		return (0);
 	}
 
-	if (bcmp(portable_mac, osp->os_portable_mac, ZIO_OBJSET_MAC_LEN) != 0 ||
-	    bcmp(local_mac, osp->os_local_mac, ZIO_OBJSET_MAC_LEN) != 0) {
-		abd_return_buf(abd, buf, datalen);
-		return (SET_ERROR(ECKSUM));
+	if (memcmp(portable_mac, osp->os_portable_mac,
+	    ZIO_OBJSET_MAC_LEN) != 0 ||
+	    memcmp(local_mac, osp->os_local_mac, ZIO_OBJSET_MAC_LEN) != 0) {
+		/*
+		 * If the MAC is zeroed out, we failed to decrypt it.
+		 * This should only arise, at least on Linux,
+		 * if we hit edge case handling for useraccounting, since we
+		 * shouldn't get here without bailing out on error earlier
+		 * otherwise.
+		 *
+		 * So if we're in that case, we can just fall through and
+		 * special-casing noticing that it's zero will handle it
+		 * elsewhere, since we can just regenerate it.
+		 */
+		if (memcmp(local_mac, zeroed_mac, ZIO_OBJSET_MAC_LEN) != 0) {
+			abd_return_buf(abd, buf, datalen);
+			return (SET_ERROR(ECKSUM));
+		}
 	}
 
 	abd_return_buf(abd, buf, datalen);