On Wed, 2012-03-28 at 11:42 -0400, Leonardo Chiquitto wrote:
> On Tue, Mar 27, 2012 at 8:48 PM, Ian Kent <raven@xxxxxxxxxx> wrote:
> > On Wed, 2012-03-28 at 08:26 +0800, Ian Kent wrote:
> >> On Thu, 2012-03-15 at 23:15 -0400, Leonardo Chiquitto wrote:
> >> >
> >> > Fix segfault in get_query_dn()
> >> >
> >> > Automount will segfault when two threads run get_query_dn()
> >> > simultaneously and $SEARCH_BASE is defined in sysconfig.
> >> > This happens because a thread tries to dereference ctxt->sdns
> >> > while another thread running the same function frees the
> >> > memory.
> >> >
> >> > I believe we don't need to reread $SEARCH_BASE every time
> >> > get_query_dn() is called.
> >> >
> >> > diff --git a/modules/lookup_ldap.c b/modules/lookup_ldap.c
> >> > index b6875fe..6ed3e17 100644
> >> > --- a/modules/lookup_ldap.c
> >> > +++ b/modules/lookup_ldap.c
> >> > @@ -281,7 +281,6 @@ static int get_query_dn(unsigned logopt, LDAP
> >> > *ldap, struct lookup_context *ctxt
> >> > char buf[MAX_ERR_BUF];
> >> > char *query, *dn, *qdn;
> >> > LDAPMessage *result = NULL, *e;
> >> > - struct ldap_searchdn *sdns = NULL;
> >> > char *attrs[2];
> >> > struct berval **value;
> >> > int scope;
> >> > @@ -330,14 +329,8 @@ static int get_query_dn(unsigned logopt, LDAP
> >> > *ldap, struct lookup_context *ctxt
> >> > scope = LDAP_SCOPE_SUBTREE;
> >> > }
> >> >
> >> > - if (!ctxt->base) {
> >> > - sdns = defaults_get_searchdns();
> >> > - if (sdns) {
> >> > - if (ctxt->sdns)
> >> > - defaults_free_searchdns(ctxt->sdns);
> >> > - ctxt->sdns = sdns;
> >> > - }
> >> > - }
> >> > + if (!ctxt->base && !ctxt->sdns)
> >> > + ctxt->sdns = defaults_get_searchdns();
> >>
> >> While this narrows the race window and should prevent the fault, it
> >> still has a problem since ctxt->sdns can change while it is in use. The
> >> above two lines are a non-atomic read then update which can (at the
> >> least) lead to a memory leak when the if (...) is evaluated while
> >> another thread is executing defaults_get_searchdns().
> >>
> >> So a mutex is still needed around these two lines.
> >>
> >
> > An even better approach would be to move the read of the search dns to
> > the lookup_init() module function. That should still do what is needed
> > and reduce the code executed at lookup a little.
> >
> > autofs-5.0.6 - fix segfault in get_query_dn()
> >
> > From: Leonardo Chiquitto <leonardo.lists@xxxxxxxxx>
> >
> > Automount will segfault when two threads run get_query_dn()
> > simultaneously and $SEARCH_BASE is defined in sysconfig.
> > This happens because a thread tries to dereference ctxt->sdns
> > while another thread running the same function frees the
> > memory.
> >
> > I believe we don't need to reread $SEARCH_BASE every time
> > get_query_dn() is called.
> >
> > edit: Ian Kent <raven@xxxxxxxxxx>
> > move the read of configured search dns to lookup_init().
> > edit end
> > ---
>
> Thanks for the updated patch, Ian. I verified that it also resolves
> the problem (I know it's obvious but, as the test case is trivial,
> I wanted to verify).
Ha, disregard my last comment, I'm still half asleep, I'll actually
commit this.
>
> Leonardo
>
> > modules/lookup_ldap.c | 13 +++----------
> > 1 files changed, 3 insertions(+), 10 deletions(-)
> >
> >
> > diff --git a/modules/lookup_ldap.c b/modules/lookup_ldap.c
> > index b6875fe..8d12920 100644
> > --- a/modules/lookup_ldap.c
> > +++ b/modules/lookup_ldap.c
> > @@ -281,7 +281,6 @@ static int get_query_dn(unsigned logopt, LDAP *ldap, struct lookup_context *ctxt
> > char buf[MAX_ERR_BUF];
> > char *query, *dn, *qdn;
> > LDAPMessage *result = NULL, *e;
> > - struct ldap_searchdn *sdns = NULL;
> > char *attrs[2];
> > struct berval **value;
> > int scope;
> > @@ -330,15 +329,6 @@ static int get_query_dn(unsigned logopt, LDAP *ldap, struct lookup_context *ctxt
> > scope = LDAP_SCOPE_SUBTREE;
> > }
> >
> > - if (!ctxt->base) {
> > - sdns = defaults_get_searchdns();
> > - if (sdns) {
> > - if (ctxt->sdns)
> > - defaults_free_searchdns(ctxt->sdns);
> > - ctxt->sdns = sdns;
> > - }
> > - }
> > -
> > dn = NULL;
> > if (!ctxt->sdns) {
> > rv = ldap_search_s(ldap, ctxt->base,
> > @@ -1467,6 +1457,9 @@ int lookup_init(const char *mapfmt, int argc, const char *const *argv, void **co
> > return 1;
> > }
> >
> > + if (!ctxt->base)
> > + ctxt->sdns = defaults_get_searchdns();
> > +
> > ctxt->timeout = defaults_get_ldap_timeout();
> > ctxt->network_timeout = defaults_get_ldap_network_timeout();
> >
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