Re: FAILED: patch "[PATCH] bpf,perf: Fix invalid prog_array access in" failed to apply to 5.15-stable tree

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Dec 16, 2024 at 10:39:46AM +0100, Jiri Olsa wrote:
> On Sun, Dec 15, 2024 at 10:02:07AM +0100, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 5.15-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> 
> hi,
> there's conflict because 5.15.y is not getting [1] fix (because 5.15.y does not have [2]),
> I'll send new backport

after digging deeper I don't think we need this fix on 5.15, because we don't
have [1] in 5.15, which allows to inherit tracing programs, in this hunk:

	 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
	-               if (overflow_handler == bpf_overflow_handler) {
	+               if (parent_event->prog) {
				struct bpf_prog *prog = parent_event->prog;

				bpf_prog_inc(prog);
				event->prog = prog;

before this fix (5.15) we allow it only for perf_event programs, which is safe,
I'll check and send separate upstream fix to handle attr.inherit for tracing
programs

thanks,
jirka


[1] f11f10bfa1ca perf/bpf: Call BPF handler directly, not through overflow machinery


> 
> jirka
> 
> 
> [1] ef1b808e3b7c bpf: Fix UAF via mismatching bpf_prog/attachment RCU flavors
> [2] 8c7dcb84e3b7 bpf: implement sleepable uprobes by chaining gps
> 
> > 
> > To reproduce the conflict and resubmit, you may use the following commands:
> > 
> > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> > git checkout FETCH_HEAD
> > git cherry-pick -x 978c4486cca5c7b9253d3ab98a88c8e769cb9bbd
> > # <resolve conflicts, build, test, etc.>
> > git commit -s
> > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024121506-pancreas-mosaic-0ae0@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
> > 
> > Possible dependencies:
> > 
> > 
> > 
> > thanks,
> > 
> > greg k-h
> > 
> > ------------------ original commit in Linus's tree ------------------
> > 
> > From 978c4486cca5c7b9253d3ab98a88c8e769cb9bbd Mon Sep 17 00:00:00 2001
> > From: Jiri Olsa <jolsa@kernel.org>
> > Date: Sun, 8 Dec 2024 15:25:07 +0100
> > Subject: [PATCH] bpf,perf: Fix invalid prog_array access in
> >  perf_event_detach_bpf_prog
> > 
> > Syzbot reported [1] crash that happens for following tracing scenario:
> > 
> >   - create tracepoint perf event with attr.inherit=1, attach it to the
> >     process and set bpf program to it
> >   - attached process forks -> chid creates inherited event
> > 
> >     the new child event shares the parent's bpf program and tp_event
> >     (hence prog_array) which is global for tracepoint
> > 
> >   - exit both process and its child -> release both events
> >   - first perf_event_detach_bpf_prog call will release tp_event->prog_array
> >     and second perf_event_detach_bpf_prog will crash, because
> >     tp_event->prog_array is NULL
> > 
> > The fix makes sure the perf_event_detach_bpf_prog checks prog_array
> > is valid before it tries to remove the bpf program from it.
> > 
> > [1] https://lore.kernel.org/bpf/Z1MR6dCIKajNS6nU@krava/T/#m91dbf0688221ec7a7fc95e896a7ef9ff93b0b8ad
> > 
> > Fixes: 0ee288e69d03 ("bpf,perf: Fix perf_event_detach_bpf_prog error handling")
> > Reported-by: syzbot+2e0d2840414ce817aaac@syzkaller.appspotmail.com
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> > Link: https://lore.kernel.org/bpf/20241208142507.1207698-1-jolsa@kernel.org
> > 
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index a403b05a7091..1b8db5aee9d3 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -2250,6 +2250,9 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
> >  		goto unlock;
> >  
> >  	old_array = bpf_event_rcu_dereference(event->tp_event->prog_array);
> > +	if (!old_array)
> > +		goto put;
> > +
> >  	ret = bpf_prog_array_copy(old_array, event->prog, NULL, 0, &new_array);
> >  	if (ret < 0) {
> >  		bpf_prog_array_delete_safe(old_array, event->prog);
> > @@ -2258,6 +2261,7 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
> >  		bpf_prog_array_free_sleepable(old_array);
> >  	}
> >  
> > +put:
> >  	/*
> >  	 * It could be that the bpf_prog is not sleepable (and will be freed
> >  	 * via normal RCU), but is called from a point that supports sleepable
> >