On Mon, Jul 08, 2019 at 01:04:59PM +0100, Daniel P. Berrangé wrote:
On Mon, Jul 08, 2019 at 01:12:06PM +0200, Michal Privoznik wrote:
On 7/8/19 12:39 PM, Daniel P. Berrangé wrote:
Neither the sasl_client_init or sasl_server_init methods are even remotely threadsafe. They do a bunch of one-time initialization and merely use a simple integer counter to avoid repeated work, not even using atomic increment/reads on the counter. This can easily race in a threaded program. Protect the calls using a virOnce initializer function which is guaranteed threadsafe at least from libvirt's POV.
If the application using libvirt also uses another library that makes use of SASL then the race still exists. It is impossible to fix that fully except in SASL code itself.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- src/rpc/virnetsaslcontext.c | 50 ++++++++++++++++++++++++------------- 1 file changed, 33 insertions(+), 17 deletions(-)
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Thanks Sahid for the report!
FYI i wrote a simple demo program that can reliably reproduce the problem in isolation
Also tested in my side, the patch well fixed the issue. Thanks Daniel and Michal. s.
Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
#include <libvirt/libvirt.h> #include <stdio.h> #include <pthread.h> #include <unistd.h>
pthread_cond_t condReady; pthread_cond_t condRun; pthread_mutex_t lock; int running;
void *runme(void *arg) { virConnectPtr conn;
pthread_mutex_lock(&lock); running++; fprintf(stderr, "Notifying we are ready\n"); pthread_cond_signal(&condReady); pthread_cond_wait(&condRun, &lock); pthread_mutex_unlock(&lock); fprintf(stderr, "Opening libvirt\n"); conn = virConnectOpenAuth("qemu:///system", virConnectAuthPtrDefault, 0); fprintf(stderr, "Open %s\n", conn ? virConnectGetURI(conn) : "failed"); if (conn) virConnectClose(conn); }
int main(int argc, char **argv) { int i; pthread_t th[20];
pthread_mutex_init(&lock, NULL); pthread_cond_init(&condRun, NULL); pthread_cond_init(&condReady, NULL);
for (i = 0; i < 20; i++) { pthread_create(&th[i], NULL, runme, NULL); }
fprintf(stderr, "Waiting for threads to initialize\n"); pthread_mutex_lock(&lock); while (running != 20) pthread_cond_wait(&condReady, &lock); fprintf(stderr, "Telling threads to proceed\n"); pthread_cond_broadcast(&condRun); pthread_mutex_unlock(&lock);
for (i = 0; i < 20; i++) { pthread_join(th[i], NULL); } return 0; }