[libvirt PATCH v2 1/1] virThreadPoolNewFull: Prevent expanding worker pool by zero

[Tim Wiederhake]

On libvirtd startup, the list of priority worker threads is uninitialized
(`pool->prioWorkers` is NULL), and then "expanded" to zero (`prioWorkers`)
entries.

This causes `virThreadPoolExpand` to call `VIR_EXPAND_N` on a null pointer
and an increment of zero. The zero increment triggers `virReallocN` to not
actually allocate any memory and leave the pointer NULL, which, eventually,
causes `memset(NULL, 0, 0)` to be called in `virExpandN`.

`memset` is declared `__attribute__ ((__nonnull__ 1))`, which triggers the
following warning when libvirt is compiled with address sanitizing enabled:

    $ meson -Dbuildtype=debug -Db_lundef=false -Db_sanitize=address,undefined
    build && ninja -C build
    $ ./build/run build/src/libvirtd
    src/util/viralloc.c:82:5: runtime error: null pointer passed as
    argument 1, which is declared to never be null

Signed-off-by: Tim Wiederhake <twiederh at redhat.com>
---
 src/util/virthreadpool.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/util/virthreadpool.c b/src/util/virthreadpool.c
index 9ddd86a679..92b7cac286 100644
--- a/src/util/virthreadpool.c
+++ b/src/util/virthreadpool.c
@@ -247,10 +247,10 @@ virThreadPoolNewFull(size_t minWorkers,
     pool->maxWorkers = maxWorkers;
     pool->maxPrioWorkers = prioWorkers;
 
-    if (virThreadPoolExpand(pool, minWorkers, false) < 0)
+    if ((minWorkers > 0) && virThreadPoolExpand(pool, minWorkers, false) < 0)
         goto error;
 
-    if (virThreadPoolExpand(pool, prioWorkers, true) < 0)
+    if ((prioWorkers > 0) && virThreadPoolExpand(pool, prioWorkers, true) < 0)
         goto error;
 
     return pool;
-- 
2.31.1