[merged mm-nonmm-stable] uprobes-revert-ref_ctr_offset-in-uprobe_unregister-error-path.patch removed from -mm tree

[merged mm-nonmm-stable] uprobes-revert-ref_ctr_offset-in-uprobe_unregister-error-path.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: uprobes: revert ref_ctr_offset in uprobe_unregister error path
has been removed from the -mm tree.  Its filename was
     uprobes-revert-ref_ctr_offset-in-uprobe_unregister-error-path.patch

This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Jiri Olsa <olsajiri@gmail.com>
Subject: uprobes: revert ref_ctr_offset in uprobe_unregister error path
Date: Wed, 14 May 2025 12:18:09 +0200

There's error path that could lead to inactive uprobe:

  1) uprobe_register succeeds - updates instruction to int3 and
     changes ref_ctr from 0 to 1
  2) uprobe_unregister fails  - int3 stays in place, but ref_ctr
     is changed to 0 (it's not restored to 1 in the fail path)
     uprobe is leaked
  3) another uprobe_register comes and re-uses the leaked uprobe
     and succeds - but int3 is already in place, so ref_ctr update
     is skipped and it stays 0 - uprobe CAN NOT be triggered now
  4) uprobe_unregister fails because ref_ctr value is unexpected

Fix this by reverting the updated ref_ctr value back to 1 in step 2),
which is the case when uprobe_unregister fails (int3 stays in place), but
we have already updated refctr.

The new scenario will go as follows:

  1) uprobe_register succeeds - updates instruction to int3 and
     changes ref_ctr from 0 to 1
  2) uprobe_unregister fails  - int3 stays in place and ref_ctr
     is reverted to 1..  uprobe is leaked
  3) another uprobe_register comes and re-uses the leaked uprobe
     and succeds - but int3 is already in place, so ref_ctr update
     is skipped and it stays 1 - uprobe CAN be triggered now
  4) uprobe_unregister succeeds

Link: https://lkml.kernel.org/r/20250514101809.2010193-1-jolsa@kernel.org
Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count (semaphore)")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/events/uprobes.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/events/uprobes.c~uprobes-revert-ref_ctr_offset-in-uprobe_unregister-error-path
+++ a/kernel/events/uprobes.c
@@ -581,8 +581,8 @@ retry:
 
 out:
 	/* Revert back reference counter if instruction update failed. */
-	if (ret < 0 && is_register && ref_ctr_updated)
-		update_ref_ctr(uprobe, mm, -1);
+	if (ret < 0 && ref_ctr_updated)
+		update_ref_ctr(uprobe, mm, is_register ? -1 : 1);
 
 	/* try collapse pmd for compound page */
 	if (ret > 0)
_

Patches currently in -mm which might be from olsajiri@gmail.com are