linux-kernel - [GIT PULL] ftrace: Return the first found result in lookup

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Date:   Wed, 11 Mar 2020 10:45:36 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Artem Savkov <asavkov@...hat.com>
Subject: [GIT PULL] ftrace: Return the first found result in lookup_rec()


Linus,

Have ftrace lookup_rec() return a consistent record otherwise it
can break live patching.


Please pull the latest trace-v5.6-rc4 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v5.6-rc4

Tag SHA1: 3bedd0c3802cdffacf9fd6a4cac9f3fa6a4da477
Head SHA1: d9815bff6b379ff46981bea9dfeb146081eab314


Artem Savkov (1):
      ftrace: Return the first found result in lookup_rec()

----
 kernel/trace/ftrace.c | 2 ++
 1 file changed, 2 insertions(+)
---------------------------
commit d9815bff6b379ff46981bea9dfeb146081eab314
Author: Artem Savkov <asavkov@...hat.com>
Date:   Fri Mar 6 18:43:17 2020 +0100

    ftrace: Return the first found result in lookup_rec()
    
    It appears that ip ranges can overlap so. In that case lookup_rec()
    returns whatever results it got last even if it found nothing in last
    searched page.
    
    This breaks an obscure livepatch late module patching usecase:
      - load livepatch
      - load the patched module
      - unload livepatch
      - try to load livepatch again
    
    To fix this return from lookup_rec() as soon as it found the record
    containing searched-for ip. This used to be this way prior lookup_rec()
    introduction.
    
    Link: http://lkml.kernel.org/r/20200306174317.21699-1-asavkov@redhat.com
    
    Cc: stable@...r.kernel.org
    Fixes: 7e16f581a817 ("ftrace: Separate out functionality from ftrace_location_range()")
    Signed-off-by: Artem Savkov <asavkov@...hat.com>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3f7ee102868a..fd81c7de77a7 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1547,6 +1547,8 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
 		rec = bsearch(&key, pg->records, pg->index,
 			      sizeof(struct dyn_ftrace),
 			      ftrace_cmp_recs);
+		if (rec)
+			break;
 	}
 	return rec;
 }