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Re: [PATCH] Fixed segfault when switching off master process during upgrade

Roman Arutyunyan
November 24, 2022 04:12AM
Hi,

On Wed, Nov 23, 2022 at 11:52:00PM +0300, Maxim Dounin wrote:
> Hello!
>
> On Wed, Nov 23, 2022 at 05:56:25PM +0400, Roman Arutyunyan wrote:
>
> > Hi,
> >
> > On Sun, Oct 30, 2022 at 05:42:33AM +0300, Maxim Dounin wrote:
> > > # HG changeset patch
> > > # User Maxim Dounin <mdounin@mdounin.ru>
> > > # Date 1667097733 -10800
> > > # Sun Oct 30 05:42:13 2022 +0300
> > > # Node ID ef9c94be7fe4685f0eeee41f76b964ea252f519f
> > > # Parent b73d95226c84b93e51f23f7b35782d98d3b516b9
> > > Fixed segfault when switching off master process during upgrade.
> > >
> > > Binary upgrades are not supported without master process, but it is,
> > > however, possible, that nginx running with master process is asked
> > > to upgrade binary, and the configuration file as available on disk
> > > at this time includes "master_process off;".
> > >
> > > If this happens, listening sockets inherited from the previous binary
> > > will have ls[i].previous set. But the old cycle on initial process
> > > startup, including startup after binary upgrade, is destroyed by
> > > ngx_init_cycle() once configuration parsing is complete. As a result,
> > > an attempt to dereference ls[i].previous in ngx_event_process_init()
> > > accesses already freed memory.
> > >
> > > Fix is to avoid looking into ls[i].previous if the old cycle is already
> > > freed.
> > >
> > > diff --git a/src/event/ngx_event.c b/src/event/ngx_event.c
> > > --- a/src/event/ngx_event.c
> > > +++ b/src/event/ngx_event.c
> > > @@ -813,7 +813,9 @@ ngx_event_process_init(ngx_cycle_t *cycl
> > > rev->deferred_accept = ls[i].deferred_accept;
> > > #endif
> > >
> > > - if (!(ngx_event_flags & NGX_USE_IOCP_EVENT)) {
> > > + if (!(ngx_event_flags & NGX_USE_IOCP_EVENT)
> > > + && cycle->old_cycle)
> > > + {
> > > if (ls[i].previous) {
> > >
> > > /*
> >
> > Doesn't this also mean that we can throw away zeroing ls->previous?
> >
> > diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
> > --- a/src/os/unix/ngx_process_cycle.c
> > +++ b/src/os/unix/ngx_process_cycle.c
> > @@ -888,15 +888,6 @@ ngx_worker_process_init(ngx_cycle_t *cyc
> > tp = ngx_timeofday();
> > srandom(((unsigned) ngx_pid << 16) ^ tp->sec ^ tp->msec);
> >
> > - /*
> > - * disable deleting previous events for the listening sockets because
> > - * in the worker processes there are no events at all at this point
> > - */
> > - ls = cycle->listening.elts;
> > - for (i = 0; i < cycle->listening.nelts; i++) {
> > - ls[i].previous = NULL;
> > - }
> > -
> > for (i = 0; cycle->modules[i]; i++) {
> > if (cycle->modules[i]->init_process) {
> > if (cycle->modules[i]->init_process(cycle) == NGX_ERROR) {
> >
>
> Yes, this code is now redundant. Added to the patch, with the
> following paragraph in the commit log:
>
> : With this change it is also no longer needed to clear ls[i].previous in
> : worker processes, so the relevant code was removed.
>
> Full patch:
>
> # HG changeset patch
> # User Maxim Dounin <mdounin@mdounin.ru>
> # Date 1669236533 -10800
> # Wed Nov 23 23:48:53 2022 +0300
> # Node ID 8852f39311de9913435fb2f2fc601a3655f42a99
> # Parent 09463dd9c50463e35856a3bd6b57bc6ca382e6f0
> Fixed segfault when switching off master process during upgrade.
>
> Binary upgrades are not supported without master process, but it is,
> however, possible, that nginx running with master process is asked
> to upgrade binary, and the configuration file as available on disk
> at this time includes "master_process off;".
>
> If this happens, listening sockets inherited from the previous binary
> will have ls[i].previous set. But the old cycle on initial process
> startup, including startup after binary upgrade, is destroyed by
> ngx_init_cycle() once configuration parsing is complete. As a result,
> an attempt to dereference ls[i].previous in ngx_event_process_init()
> accesses already freed memory.
>
> Fix is to avoid looking into ls[i].previous if the old cycle is already
> freed.
>
> With this change it is also no longer needed to clear ls[i].previous in
> worker processes, so the relevant code was removed.
>
> diff --git a/src/event/ngx_event.c b/src/event/ngx_event.c
> --- a/src/event/ngx_event.c
> +++ b/src/event/ngx_event.c
> @@ -813,7 +813,9 @@ ngx_event_process_init(ngx_cycle_t *cycl
> rev->deferred_accept = ls[i].deferred_accept;
> #endif
>
> - if (!(ngx_event_flags & NGX_USE_IOCP_EVENT)) {
> + if (!(ngx_event_flags & NGX_USE_IOCP_EVENT)
> + && cycle->old_cycle)
> + {
> if (ls[i].previous) {
>
> /*
> diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
> --- a/src/os/unix/ngx_process_cycle.c
> +++ b/src/os/unix/ngx_process_cycle.c
> @@ -759,7 +759,6 @@ ngx_worker_process_init(ngx_cycle_t *cyc
> ngx_cpuset_t *cpu_affinity;
> struct rlimit rlmt;
> ngx_core_conf_t *ccf;
> - ngx_listening_t *ls;
>
> if (ngx_set_environment(cycle, NULL) == NULL) {
> /* fatal */
> @@ -889,15 +888,6 @@ ngx_worker_process_init(ngx_cycle_t *cyc
> tp = ngx_timeofday();
> srandom(((unsigned) ngx_pid << 16) ^ tp->sec ^ tp->msec);
>
> - /*
> - * disable deleting previous events for the listening sockets because
> - * in the worker processes there are no events at all at this point
> - */
> - ls = cycle->listening.elts;
> - for (i = 0; i < cycle->listening.nelts; i++) {
> - ls[i].previous = NULL;
> - }
> -
> for (i = 0; cycle->modules[i]; i++) {
> if (cycle->modules[i]->init_process) {
> if (cycle->modules[i]->init_process(cycle) == NGX_ERROR) {

Looks good.

--
Roman Arutyunyan
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Subject Author Views Posted

[PATCH] Fixed segfault when switching off master process during upgrade

Maxim Dounin 663 October 29, 2022 10:44PM

Re: [PATCH] Fixed segfault when switching off master process during upgrade

Maxim Dounin 109 November 18, 2022 08:58AM

Re: [PATCH] Fixed segfault when switching off master process during upgrade

Roman Arutyunyan 102 November 23, 2022 08:58AM

Re: [PATCH] Fixed segfault when switching off master process during upgrade

Maxim Dounin 104 November 23, 2022 03:54PM

Re: [PATCH] Fixed segfault when switching off master process during upgrade

Roman Arutyunyan 113 November 24, 2022 04:12AM

Re: [PATCH] Fixed segfault when switching off master process during upgrade

Maxim Dounin 177 November 24, 2022 01:28PM



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