Date: Sun, 27 Mar 2011 23:49:15 +0300 From: Mikolaj Golub <trociny@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r220062 - head/sys/geom/gate Message-ID: <86fwq8e1bo.fsf@kopusha.home.net> In-Reply-To: <20110327200804.GM78089@deviant.kiev.zoral.com.ua> (Kostik Belousov's message of "Sun, 27 Mar 2011 23:08:04 %2B0300") References: <201103271956.p2RJutha067490@svn.freebsd.org> <20110327200804.GM78089@deviant.kiev.zoral.com.ua>
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On Sun, 27 Mar 2011 23:08:04 +0300 Kostik Belousov wrote: KB> On Sun, Mar 27, 2011 at 07:56:55PM +0000, Mikolaj Golub wrote: >> Author: trociny >> Date: Sun Mar 27 19:56:55 2011 >> New Revision: 220062 >> URL: http://svn.freebsd.org/changeset/base/220062 >> >> Log: >> In g_gate_create() there is a window between when g_gate_softc is >> registered in g_gate_units array and when its sc_provider field is >> filled. If during this period g_gate_units is accessed by another >> thread that is checking for provider name collision the crash is >> possible. >> >> Fix this by adding sc_name field to struct g_gate_softc. In >> g_gate_create() when g_gate_softc is created but sc_provider is still >> not sc_name points to provider name stored in the local array. >> >> Approved by: pjd (mentor) >> Reported by: Freddie Cash <fjwcash@gmail.com> >> MFC after: 1 week >> >> Modified: >> head/sys/geom/gate/g_gate.c >> head/sys/geom/gate/g_gate.h >> >> Modified: head/sys/geom/gate/g_gate.c >> ============================================================================== >> --- head/sys/geom/gate/g_gate.c Sun Mar 27 19:29:18 2011 (r220061) >> +++ head/sys/geom/gate/g_gate.c Sun Mar 27 19:56:55 2011 (r220062) >> @@ -409,13 +409,14 @@ g_gate_create(struct g_gate_ctl_create * >> for (unit = 0; unit < g_gate_maxunits; unit++) { >> if (g_gate_units[unit] == NULL) >> continue; >> - if (strcmp(name, g_gate_units[unit]->sc_provider->name) != 0) >> + if (strcmp(name, g_gate_units[unit]->sc_name) != 0) >> continue; >> mtx_unlock(&g_gate_units_lock); >> mtx_destroy(&sc->sc_queue_mtx); >> free(sc, M_GATE); >> return (EEXIST); >> } >> + sc->sc_name = name; >> g_gate_units[sc->sc_unit] = sc; >> g_gate_nunits++; >> mtx_unlock(&g_gate_units_lock); >> @@ -434,6 +435,9 @@ g_gate_create(struct g_gate_ctl_create * >> sc->sc_provider = pp; >> g_error_provider(pp, 0); >> g_topology_unlock(); >> + mtx_lock(&g_gate_units_lock); >> + sc->sc_name = sc->sc_provider->name; >> + mtx_unlock(&g_gate_units_lock); KB> I think you do not need a mutex locked around the single assignment. KB> As I understand, sc_provider->name is constant ? Is the following scenario impossible? Thread A is looking for name collision and is accessing g_gate_units[unit]->sc_name of the unit that is being created by a thread B, so sc_name is pointing to thread B local buffer. At this time the thread B creates provider, does sc->sc_name = sc->sc_provider->name and returns from g_gate_create(). Thread A, if it is still working with g_gate_units[unit]->sc_name, is accessing invalid memory. -- Mikolaj Golub
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