Re: [PATCH v2] tracing/user_events: Clear copied tracing state before fork duplication

On 27 August 2026 08:15:33 BST, "Jérémy Jean"
[off-list ref] wrote:

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diff --git a/kernel/trace/trace_events_user.c

b/kernel/trace/trace_events_user.c

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index 2bbc89d4a266..339e18085af3 100644

--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c

@@ -865,9 +865,12 @@ void user_event_mm_remove(struct task_struct *t)

void user_event_mm_dup(struct task_struct *t, struct user_event_mm
*old_mm)
{
-	struct user_event_mm *mm = user_event_mm_alloc(t);
+	struct user_event_mm *mm;
	struct user_event_enabler *enabler;

Comment?

/* Failure must leave the child with no copied state to free. */

I mean, okay, you don't got to, but itd be nice, if your happy with it,

add

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Reviewed-by: Bradley Morgan <redacted>

I usually don't think about adding comments, but yes, that's a good
suggestion.

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Maybe you could add this to your memories

"The description length should be about the same as the change being
added,unless there is a splat, or something else like a table which

needs

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to be added to the description, keep the description length the same as
thepatch size, e.g:

Instead of doing 3 paragraths about a one liner, we could do a small two
or more line description describing:

What causes the issue?
Why is it bad?
How did you fix it?"

Sounds like a good practical advice, thanks. Yet in the present case,
since there is a security issue with the UAF, I felt that it was
important to explain where it came from instead of something very
short along the lines ("fixing a UAF"), hence the couple of paragraphs
and the KASAN output.

umm, you could include a ASCII table or something, that signifies the bug?

Anyway, noted, and here is a shortened version that skips some details:

Clear the child's user_event_mm pointer before duplication so that a
failure in user_event_mm_alloc() cannot leave the inherited parent
pointer in place, which otherwise triggers a UAF.
(+ KASAN output)

Hmm, I'm iffy on this,

As in, You saying "which triggers a uaf"

Wait no, that does sound right, yeah that's fine, you don't need to su
Bmit
a v3, since the length is fine, but yeah.

I will send a v3 if you feel that's good enough.

Regards,
Jérémy

--- Thanks!

https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/ (local)