perf: Disallow mis-matched inherited group reads
authorPeter Zijlstra <peterz@infradead.org>
Wed, 18 Oct 2023 11:56:54 +0000 (13:56 +0200)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 25 Oct 2023 10:03:15 +0000 (12:03 +0200)
commitf6952655a61264900ed08e9d642adad8222f8e29
tree1b40ea7d3435f8263d1909238419daf31f1b808d
parent908c62800584a69a474b80a308bd771cc7762fb2
perf: Disallow mis-matched inherited group reads

commit 32671e3799ca2e4590773fd0e63aaa4229e50c06 upstream.

Because group consistency is non-atomic between parent (filedesc) and children
(inherited) events, it is possible for PERF_FORMAT_GROUP read() to try and sum
non-matching counter groups -- with non-sensical results.

Add group_generation to distinguish the case where a parent group removes and
adds an event and thus has the same number, but a different configuration of
events as inherited groups.

This became a problem when commit fa8c269353d5 ("perf/core: Invert
perf_read_group() loops") flipped the order of child_list and sibling_list.
Previously it would iterate the group (sibling_list) first, and for each
sibling traverse the child_list. In this order, only the group composition of
the parent is relevant. By flipping the order the group composition of the
child (inherited) events becomes an issue and the mis-match in group
composition becomes evident.

That said; even prior to this commit, while reading of a group that is not
equally inherited was not broken, it still made no sense.

(Ab)use ECHILD as error return to indicate issues with child process group
composition.

Fixes: fa8c269353d5 ("perf/core: Invert perf_read_group() loops")
Reported-by: Budimir Markovic <markovicbudimir@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20231018115654.GK33217@noisy.programming.kicks-ass.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
include/linux/perf_event.h
kernel/events/core.c