linux-kernel - [PATCH v2 0/2] tracing/user_events: Fix non-spaced field matching

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Message-Id: <20240423162338.292-1-beaub@linux.microsoft.com>
Date: Tue, 23 Apr 2024 16:23:36 +0000
From: Beau Belgrave <beaub@...ux.microsoft.com>
To: rostedt@...dmis.org,
	mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com
Cc: linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	dcook@...ux.microsoft.com
Subject: [PATCH v2 0/2] tracing/user_events: Fix non-spaced field matching

When the ABI was updated to prevent same name w/different args, it
missed an important corner case when fields don't end with a space.
Typically, space is used for fields to help separate them, like
"u8 field1; u8 field2". If no spaces are used, like
"u8 field1;u8 field2", then the parsing works for the first time.
However, the match check fails on a subsequent register, leading to
confusion.

This is because the match check uses argv_split() and assumes that all
fields will be split upon the space. When spaces are used, we get back
{ "u8", "field1;" }, without spaces we get back { "u8", "field1;u8" }.
This causes a mismatch, and the user program gets back -EADDRINUSE.

Add a method to detect this case before calling argv_split(). If found
force a space after the field separator character ';'. This ensures all
cases work properly for matching.

I could not find an existing function to accomplish this, so I had to
hand code a copy with this logic. If there is a better way to achieve
this, I'm all ears.

This series also adds a selftest to ensure this doesn't break again.

With this fix, the following are all treated as matching:
u8 field1;u8 field2
u8 field1; u8 field2
u8 field1;\tu8 field2
u8 field1;\nu8 field2

V2 changes:
  Renamed fix_semis_no_space() to insert_space_after_semis().
  Have user_event_argv_split() return fast in no-split case.
  Pulled in Masami's shorter loop in insert_space_after_semis().

Beau Belgrave (2):
  tracing/user_events: Fix non-spaced field matching
  selftests/user_events: Add non-spacing separator check

 kernel/trace/trace_events_user.c              | 76 ++++++++++++++++++-
 .../selftests/user_events/ftrace_test.c       |  8 ++
 2 files changed, 83 insertions(+), 1 deletion(-)

base-commit: 0bbac3facb5d6cc0171c45c9873a2dc96bea9680
-- 
2.34.1