From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E31F2296D20; Mon, 14 Apr 2025 13:29:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744637341; cv=none; b=DjKjHcD5qNeLG4E2HA65Km/pC56mTZBlXi8fQom5YYmIXf5bZ80ftiPTTQYBVvJm8bBfqvJEEEo5O8EaCEn/MdEIZxPO6OTZ5uYPSD4nmjMO1SFJVGRVRQGvkK/KtcHRY9YSW6wlHoTrV9v+JRDmhPahKOMHffBBQKAO+W6JC/k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744637341; c=relaxed/simple; bh=kr0x5q95iVOK8rO660x057UTx55vVWd9whQuL7WCzQU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=H4jRE0JDzbN2Qa30HIS1VXIYlRwqazRHEAU0p06l0IiaMA6js6WDzksjFYRi6GbGVVQSHLPJv5ENVJ3KBoP+Yo6uJyfW9sTkoNEm7krIiHKbLu1/CMH3dbMeQQV2kdxbvdHMJya/eL1XLtjhMTco8G3DJycamD1mQpTG6nTTYdA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SVGEFFiU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SVGEFFiU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C1CBBC4CEEB; Mon, 14 Apr 2025 13:28:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744637340; bh=kr0x5q95iVOK8rO660x057UTx55vVWd9whQuL7WCzQU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SVGEFFiUyLegU73jeagMHQw5e3U4OZXVvOYECuzdUmduwRuukL44oSp2352hgcWs7 hH0GOLp7TISTi7w26fZdz4XElAMBoWyivFdX4yBTwmTXy9TdzcV4DblTYXkWTjajkN 8MUwGgah7EZe3GlGGsmoeDAuK3fyLb+F/HBtIooEuxOUOVghCdSLG6KqnjPvRxaIPo 28H8GcKrAIM+rOfaM44eWoYw6tZ1KarDapePyj0XPqv1MeUB++tiwEE146nOhhFCjg crGMIUhPf96gO39EH9kPbVDJRbYMXTZN2SfYNhtFpVNigL64qV7OOGVvP3bZiArsWG XEuxKs6gNDINw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Gabriel Shahrouzi , syzbot+ff3aa851d46ab82953a3@syzkaller.appspotmail.com, Ingo Molnar , Peter Zijlstra , Ravi Bangoria , Kan Liang , Oleg Nesterov , Alexander Shishkin , Sasha Levin , mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, linux-perf-users@vger.kernel.org Subject: [PATCH AUTOSEL 6.12 05/30] perf/core: Fix WARN_ON(!ctx) in __free_event() for partial init Date: Mon, 14 Apr 2025 09:28:22 -0400 Message-Id: <20250414132848.679855-5-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250414132848.679855-1-sashal@kernel.org> References: <20250414132848.679855-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.12.23 Content-Transfer-Encoding: 8bit From: Gabriel Shahrouzi [ Upstream commit 0ba3a4ab76fd3367b9cb680cad70182c896c795c ] Move the get_ctx(child_ctx) call and the child_event->ctx assignment to occur immediately after the child event is allocated. Ensure that child_event->ctx is non-NULL before any subsequent error path within inherit_event calls free_event(), satisfying the assumptions of the cleanup code. Details: There's no clear Fixes tag, because this bug is a side-effect of multiple interacting commits over time (up to 15 years old), not a single regression. The code initially incremented refcount then assigned context immediately after the child_event was created. Later, an early validity check for child_event was added before the refcount/assignment. Even later, a WARN_ON_ONCE() cleanup check was added, assuming event->ctx is valid if the pmu_ctx is valid. The problem is that the WARN_ON_ONCE() could trigger after the initial check passed but before child_event->ctx was assigned, violating its precondition. The solution is to assign child_event->ctx right after its initial validation. This ensures the context exists for any subsequent checks or cleanup routines, resolving the WARN_ON_ONCE(). To resolve it, defer the refcount update and child_event->ctx assignment directly after child_event->pmu_ctx is set but before checking if the parent event is orphaned. The cleanup routine depends on event->pmu_ctx being non-NULL before it verifies event->ctx is non-NULL. This also maintains the author's original intent of passing in child_ctx to find_get_pmu_context before its refcount/assignment. [ mingo: Expanded the changelog from another email by Gabriel Shahrouzi. ] Reported-by: syzbot+ff3aa851d46ab82953a3@syzkaller.appspotmail.com Signed-off-by: Gabriel Shahrouzi Signed-off-by: Ingo Molnar Cc: Peter Zijlstra Cc: Ravi Bangoria Cc: Kan Liang Cc: Oleg Nesterov Cc: Alexander Shishkin Link: https://lore.kernel.org/r/20250405203036.582721-1-gshahrouzi@gmail.com Closes: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3 Signed-off-by: Sasha Levin --- kernel/events/core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index b5ccf52bb71ba..8f0dcd8e64888 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -13622,6 +13622,9 @@ inherit_event(struct perf_event *parent_event, if (IS_ERR(child_event)) return child_event; + get_ctx(child_ctx); + child_event->ctx = child_ctx; + pmu_ctx = find_get_pmu_context(child_event->pmu, child_ctx, child_event); if (IS_ERR(pmu_ctx)) { free_event(child_event); @@ -13644,8 +13647,6 @@ inherit_event(struct perf_event *parent_event, return NULL; } - get_ctx(child_ctx); - /* * Make the child state follow the state of the parent event, * not its attr.disabled bit. We hold the parent's mutex, @@ -13666,7 +13667,6 @@ inherit_event(struct perf_event *parent_event, local64_set(&hwc->period_left, sample_period); } - child_event->ctx = child_ctx; child_event->overflow_handler = parent_event->overflow_handler; child_event->overflow_handler_context = parent_event->overflow_handler_context; -- 2.39.5