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block/nbd: fix possible use after free of s->connect_thread

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If on nbd_close() we detach the thread (in
nbd_co_establish_connection_cancel() thr->state becomes
CONNECT_THREAD_RUNNING_DETACHED), after that point we should not use
s->connect_thread (which is set to NULL), as running thread may free it
at any time.

Still nbd_co_establish_connection() does exactly this: it saves
s->connect_thread to local variable (just for better code style) and
use it even after yield point, when thread may be already detached.

Fix that. Also check thr to be non-NULL on
nbd_co_establish_connection() start for safety.

After this patch "case CONNECT_THREAD_RUNNING_DETACHED" becomes
impossible in the second switch in nbd_co_establish_connection().
Still, don't add extra abort() just before the release. If it somehow
possible to reach this "case:" it won't hurt. Anyway, good refactoring
of all this reconnect mess will come soon.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210406155114.1057355-1-vsementsov@virtuozzo.com>
Reviewed-by: Roman Kagan <rvkagan@yandex-team.ru>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2021-04-06 18:51:14 +03:00 committed by Max Reitz
parent dce628a97f
commit 0267101af6
1 changed files with 11 additions and 0 deletions
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11
block/nbd.c
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@ -443,6 +443,11 @@ nbd_co_establish_connection(BlockDriverState *bs, Error **errp)
BDRVNBDState *s = bs->opaque;
NBDConnectThread *thr = s->connect_thread;
if (!thr) {
/* detached */
return -1;
}
qemu_mutex_lock(&thr->mutex);
switch (thr->state) {
@ -486,6 +491,12 @@ nbd_co_establish_connection(BlockDriverState *bs, Error **errp)
s->wait_connect = true;
qemu_coroutine_yield();
if (!s->connect_thread) {
/* detached */
return -1;
}
assert(thr == s->connect_thread);
qemu_mutex_lock(&thr->mutex);
switch (thr->state) {