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BUG/MINOR: map/cli: make sure patterns don't vanish under "show map"'s init

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When "show map" initializes itself, it first takes the reference to the
starting point under a lock, then releases it before switching to state
STATE_LIST, and takes the lock again. The problem is that it is possible
for another thread to remove the first element during this unlock/lock
sequence, and make the list run anywhere. This is of course extremely
unlikely but not impossible.

Let's initialize the pointer in the STATE_LIST part under the same lock,
which is simpler and more reliable.

This should be backported to all versions.
This commit is contained in:
Willy Tarreau 2022-05-03 15:26:27 +02:00
parent 2edaace575
commit 1ae0c43244
1 changed files with 3 additions and 12 deletions
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15
src/map.c
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@ -345,27 +345,17 @@ static int cli_io_handler_pat_list(struct appctx *appctx)
switch (appctx->st2) {
case STAT_ST_INIT:
/* the function had not been called yet, let's prepare the
* buffer for a response. We initialize the current stream
* pointer to the first in the global list. When a target
* stream is being destroyed, it is responsible for updating
* this pointer. We know we have reached the end when this
* pointer points back to the head of the streams list.
*/
HA_SPIN_LOCK(PATREF_LOCK, &appctx->ctx.map.ref->lock);
LIST_INIT(&appctx->ctx.map.bref.users);
appctx->ctx.map.bref.ref = appctx->ctx.map.ref->head.n;
HA_SPIN_UNLOCK(PATREF_LOCK, &appctx->ctx.map.ref->lock);
appctx->st2 = STAT_ST_LIST;
/* fall through */
case STAT_ST_LIST:
HA_SPIN_LOCK(PATREF_LOCK, &appctx->ctx.map.ref->lock);
if (!LIST_ISEMPTY(&appctx->ctx.map.bref.users)) {
LIST_DELETE(&appctx->ctx.map.bref.users);
LIST_INIT(&appctx->ctx.map.bref.users);
} else {
appctx->ctx.map.bref.ref = appctx->ctx.map.ref->head.n;
}
while (appctx->ctx.map.bref.ref != &appctx->ctx.map.ref->head) {
@ -718,6 +708,7 @@ static int cli_parse_show_map(char **args, char *payload, struct appctx *appctx,
else
appctx->ctx.cli.i0 = appctx->ctx.map.ref->curr_gen;
LIST_INIT(&appctx->ctx.map.bref.users);
appctx->io_handler = cli_io_handler_pat_list;
appctx->io_release = cli_release_show_map;
return 0;