Users are seeing periodic segfaults from libvirt client apps, especially thread heavy ones like virt-manager. A typical stack trace would end up in the virNetClientIOEventFD method, with illegal access to stale stack data. eg ==238721==ERROR: AddressSanitizer: stack-use-after-return on address 0x75cd18709788 at pc 0x75cd3111f907 bp 0x75cd181ff550 sp 0x75cd181ff548 WRITE of size 4 at 0x75cd18709788 thread T11 #0 0x75cd3111f906 in virNetClientIOEventFD /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/rpc/virnetclient.c:1634:15 #1 0x75cd3210d198 (/usr/lib/libglib-2.0.so.0+0x5a198) (BuildId: 0a2311dfbbc6c215dc36f4b6bdd2b4b6fbae55a2) #2 0x75cd3216c3be (/usr/lib/libglib-2.0.so.0+0xb93be) (BuildId: 0a2311dfbbc6c215dc36f4b6bdd2b4b6fbae55a2) #3 0x75cd3210ddc6 in g_main_loop_run (/usr/lib/libglib-2.0.so.0+0x5adc6) (BuildId: 0a2311dfbbc6c215dc36f4b6bdd2b4b6fbae55a2) #4 0x75cd3111a47c in virNetClientIOEventLoop /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/rpc/virnetclient.c:1722:9 #5 0x75cd3111a47c in virNetClientIO /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/rpc/virnetclient.c:2002:10 #6 0x75cd3111a47c in virNetClientSendInternal /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/rpc/virnetclient.c:2170:11 #7 0x75cd311198a8 in virNetClientSendWithReply /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/rpc/virnetclient.c:2198:11 #8 0x75cd31111653 in virNetClientProgramCall /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/rpc/virnetclientprogram.c:318:9 #9 0x75cd31241c8f in callFull /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/remote/remote_driver.c:6054:10 #10 0x75cd31241c8f in call /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/remote/remote_driver.c:6076:12 #11 0x75cd31241c8f in remoteNetworkGetXMLDesc /usr/src/debug/libvirt/libvirt-10.2.0/build/src/remote/remote_client_bodies.h:5959:9 #12 0x75cd31410ff7 in virNetworkGetXMLDesc /usr/src/debug/libvirt/libvirt-10.2.0/build/../src/libvirt-network.c:952:15 The root cause is a bad assumption in the virNetClientIOEventLoop method. This method is run by whichever thread currently owns the buck, and is responsible for handling I/O. Inside a for(;;) loop, this method creates a temporary GSource, adds it to the event loop and runs g_main_loop_run(). When I/O is ready, the GSource callback (virNetClientIOEventFD) will fire and call g_main_loop_quit(), and return G_SOURCE_REMOVE which results in the temporary GSource being destroyed. A g_autoptr() will then remove the last reference. What was overlooked, is that a second thread can come along and while it can't enter virNetClientIOEventLoop, it will register an idle source that uses virNetClientIOWakeup to interrupt the original thread's 'g_main_loop_run' call. When this happens the virNetClientIOEventFD callback never runs, and so the temporary GSource is not destroyed. The g_autoptr() will remove a reference, but by virtue of still being attached to the event context, there is an extra reference held causing GSource to be leaked. The next time 'g_main_loop_run' is called, the original GSource will trigger its callback, and access data that was allocated on the stack by the previous thread, and likely SEGV. To solve this, the thread calling 'g_main_loop_run' must call g_source_destroy, immediately upon return, to guarantee that the temporary GSource is removed. CVE-2024-4418 Reported-by: Martin Shirokov <shirokovmartin(a)gmail.com&gt; Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; --- src/rpc/virnetclient.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/src/rpc/virnetclient.c b/src/rpc/virnetclient.c index 68098b1c8d..147b0d661a 100644 --- a/src/rpc/virnetclient.c +++ b/src/rpc/virnetclient.c @@ -1657,7 +1657,7 @@ static int virNetClientIOEventLoop(virNetClient *client, #endif /* !WIN32 */ int timeout = -1; virNetMessage *msg = NULL; - g_autoptr(GSource) G_GNUC_UNUSED source = NULL; + g_autoptr(GSource) source = NULL; GIOCondition ev = 0; struct virNetClientIOEventData data = { .client = client, @@ -1721,6 +1721,18 @@ static int virNetClientIOEventLoop(virNetClient *client, g_main_loop_run(client->eventLoop); + /* + * If virNetClientIOEventFD ran, this GSource will already be + * destroyed due to G_SOURCE_REMOVE. It is harmless to re-destroy + * it, since we still own a reference. + * + * If virNetClientIOWakeup ran, it will have interrupted the + * g_main_loop_run call, before virNetClientIOEventFD could + * run, and thus the GSource is still registered, and we need + * to destroy it since it is referencing stack memory for 'data' + */ + g_source_destroy(source); + #ifndef WIN32 ignore_value(pthread_sigmask(SIG_SETMASK, &oldmask, NULL)); #endif /* !WIN32 */ -- 2.43.0