From: Michael Adam <obnox@samba.org>
Date: Wed, 11 Apr 2012 13:48:02 +0000 (+0200)
Subject: s3:registry: fix seqnum race in fetch_values_internal
X-Git-Url: http://git.samba.org/samba.git/?p=kai%2Fsamba.git;a=commitdiff_plain;h=7ea8bd3605adb3a53ca44ebdabfdcdb9c1aeaa18

s3:registry: fix seqnum race in fetch_values_internal

This prevents race between fetching seqnum and key content.

Because there is currently no way to atomically fetch the
record along with the seqnum, I use a loop.
This is far from optimal and should should ideally be done
differently. But for now it fixes the race.

Signed-off-by: Andreas Schneider <asn@samba.org>
---

diff --git a/source3/registry/reg_backend_db.c b/source3/registry/reg_backend_db.c
index 65355aec237..abe9f7bdca5 100644
--- a/source3/registry/reg_backend_db.c
+++ b/source3/registry/reg_backend_db.c
@@ -1862,6 +1862,7 @@ static int regdb_fetch_values_internal(struct db_context *db, const char* key,
 	int ret = 0;
 	TDB_DATA value;
 	WERROR werr;
+	int seqnum[2], count;
 
 	DEBUG(10,("regdb_fetch_values: Looking for values of key [%s]\n", key));
 
@@ -1874,10 +1875,27 @@ static int regdb_fetch_values_internal(struct db_context *db, const char* key,
 		goto done;
 	}
 
-	werr = regval_ctr_set_seqnum(values, dbwrap_get_seqnum(db));
-	W_ERROR_NOT_OK_GOTO_DONE(werr);
+	ZERO_STRUCT(value);
+	count = 0;
+	seqnum[0] = dbwrap_get_seqnum(db);
+
+	do {
+		count++;
+		TALLOC_FREE(value.dptr);
+		value = regdb_fetch_key_internal(db, ctx, keystr);
+		seqnum[count % 2] = dbwrap_get_seqnum(db);
+	} while (seqnum[0] != seqnum[1]);
+
+	if (count > 1) {
+		DEBUG(5, ("regdb_fetch_values_internal: it took %d attempts "
+			  "to fetch key '%s' with constant seqnum\n",
+			  count, key));
+	}
 
-	value = regdb_fetch_key_internal(db, ctx, keystr);
+	werr = regval_ctr_set_seqnum(values, seqnum[0]);
+	if (!W_ERROR_IS_OK(werr)) {
+		goto done;
+	}
 
 	if (!value.dptr) {
 		/* all keys have zero values by default */