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tdb: Add tdb_chainwalk_check

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This captures the tdb_rescue protection against circular hash chains
with a slow pointer updated only on every other record traverse

If a hash chain has a loop, eventually the next_ptr
will cycle around and be identical to the 'slow' pointer.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
This commit is contained in:
Volker Lendecke 2018-10-04 15:20:10 +02:00 committed by Jeremy Allison
parent 5ba7b2042b
commit b83763d175
2 changed files with 39 additions and 0 deletions
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29
lib/tdb/common/tdb.c
View File

@ -79,6 +79,35 @@ static int tdb_key_compare(TDB_DATA key, TDB_DATA data, void *private_data)
return memcmp(data.dptr, key.dptr, data.dsize);
}
void tdb_chainwalk_init(struct tdb_chainwalk_ctx *ctx, tdb_off_t ptr)
{
*ctx = (struct tdb_chainwalk_ctx) { .slow_ptr = ptr };
}
bool tdb_chainwalk_check(struct tdb_context *tdb,
struct tdb_chainwalk_ctx *ctx,
tdb_off_t next_ptr)
{
int ret;
if (ctx->slow_chase) {
ret = tdb_ofs_read(tdb, ctx->slow_ptr, &ctx->slow_ptr);
if (ret == -1) {
return false;
}
}
ctx->slow_chase = !ctx->slow_chase;
if (next_ptr == ctx->slow_ptr) {
tdb->ecode = TDB_ERR_CORRUPT;
TDB_LOG((tdb, TDB_DEBUG_ERROR,
"tdb_chainwalk_check: circular chain\n"));
return false;
}
return true;
}
/* Returns 0 on fail. On success, return offset of record, and fills
in rec */
static tdb_off_t tdb_find(struct tdb_context *tdb, TDB_DATA key, uint32_t hash,

10
lib/tdb/common/tdb_private.h
View File

@ -191,6 +191,11 @@ struct tdb_lock_type {
uint32_t ltype;
};
struct tdb_chainwalk_ctx {
tdb_off_t slow_ptr;
bool slow_chase;
};
struct tdb_traverse_lock {
struct tdb_traverse_lock *next;
uint32_t off;
@ -198,6 +203,11 @@ struct tdb_traverse_lock {
int lock_rw;
};
void tdb_chainwalk_init(struct tdb_chainwalk_ctx *ctx, tdb_off_t ptr);
bool tdb_chainwalk_check(struct tdb_context *tdb,
struct tdb_chainwalk_ctx *ctx,
tdb_off_t next_ptr);
enum tdb_lock_flags {
/* WAIT == F_SETLKW, NOWAIT == F_SETLK */
TDB_LOCK_NOWAIT = 0,