Re: race condition in libports

[Samuel Thibault]

Hello,

Brent W. Baccala, on sam. 16 déc. 2017 21:37:05 -0500, wrote:
> basically, we're storing ports in a inode-to-port hash, looking them
> up when io_identity() gets called, and removing them from the hash
> when the class's clean routine gets called.

That's the bug: one needs a reference for this.  And it's a weak
reference: identity is fine with getting rid of it.  Could you try the
attached patch?

Samuel

Index: hurd-debian/libfshelp/get-identity.c
===================================================================
--- hurd-debian.orig/libfshelp/get-identity.c
+++ hurd-debian/libfshelp/get-identity.c
@@ -42,7 +43,12 @@ id_clean (void *cookie)
 {
   struct idspec *i = cookie;
   pthread_mutex_lock (&idlock);
-  hurd_ihash_locp_remove (&idhash, i->id_hashloc);
+  if (refcounts_hard_references(&i->pi.refcounts) == 0)
+    {
+      /* Nobody got a send right in between, we can remove from the hash.  */
+      hurd_ihash_locp_remove (&idhash, i->id_hashloc);
+      ports_port_deref_weak (&i->pi);
+    }
   pthread_mutex_unlock (&idlock);
 }
 
@@ -50,7 +56,7 @@ static void
 id_initialize ()
 {
   assert_backtrace (!idclass);
-  idclass = ports_create_class (id_clean, NULL);
+  idclass = ports_create_class (NULL, id_clean);
 }
 
 error_t
@@ -75,6 +81,9 @@ fshelp_get_identity (struct port_bucket
       if (err)
         goto lose_port;
 
+      /* Weak reference for the hash entry.  */
+      ports_port_ref_weak(&i->pi);
+
       *pt = ports_get_right (i);
       ports_port_deref (i);
     }