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s3:registry: fix seqnum race in fetch_values_internal

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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>
This commit is contained in:
Michael Adam 2012-04-11 15:48:02 +02:00 committed by Andreas Schneider
parent ab83005b30
commit 7ea8bd3605
1 changed files with 21 additions and 3 deletions
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24
source3/registry/reg_backend_db.c
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@ -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);
value = regdb_fetch_key_internal(db, ctx, keystr);
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));
}
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 */