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 C5A4B24466D; Sun, 14 Sep 2025 02:51:24 +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=1757818284; cv=none; b=APY+HCNRo7/hPYeUCZoKPxAr5xTKLkfENeCOfhjrJBUcwrCNI+hsPmAghDsH9FuQxLmlGcUXljK6gXaULJX+Ktr4WjlQuZLdQrcBnp/1L9pvCw6uGY/qPeQ2pv40HZVz+aPXqujEcmRhDF8pvnMSGFqTc93ZSFJDELXR9TIgMto= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757818284; c=relaxed/simple; bh=EEttELQ0YqnMfVMS6rsgMzRidkodEpmUZswFU0OhZIA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=D3SRaCrwEXqZqFbkH+f0mkImOJGAf5kbiJipD2qbq9LaTaZ4VcC2d0+Wgej7zSS/ggHGbaV34QWsR4gabeAYtVqIEi8q6oirebGsU2aW0fVizueSaLb69jqUHsYEJAj1TVhzRb+RgY3g3yKfDshRw6wTkb96DGA8DMxqjFP/gXQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ftIwtQUm; 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="ftIwtQUm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2D36BC4CEEB; Sun, 14 Sep 2025 02:51:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757818284; bh=EEttELQ0YqnMfVMS6rsgMzRidkodEpmUZswFU0OhZIA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ftIwtQUmQePnUQ84pTdM71MBHOvPs0B9rOMTYmCsk1kogvt891vc4957LB2idotK3 qRSfD53jnqWeApkO3fTuT93STDzFH5VzjdJD0W9XJ/DrEcizPE7nzgE72uS0+/a4Hc d2BUK0wXYrPY9dE829znKzNJMXTlc1G2t6HnveDRKBTSBa0wILs5/1dDDLSDY0Seq9 l1mFB+y7YZpMlJ4OEsetYoIDZ6NnBLxIyoQNiD2PLQ9DxbRobqTtQWbdiGykhzXncC a0o1nWt8UZt+YlEF+SEFgaMcCMbsZIHMXPQCRv35lCeCAzTMWgvO36orQ9yiqV1gjN IY9On+ArPn+Yw== From: SeongJae Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, Stanislav Fort , Stanislav Fort , SeongJae Park , Andrew Morton Subject: [PATCH 6.6.y] mm/damon/sysfs: fix use-after-free in state_show() Date: Sat, 13 Sep 2025 19:51:21 -0700 Message-Id: <20250914025121.2284-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <2025091318-trombone-graduate-3828@gregkh> References: <2025091318-trombone-graduate-3828@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Stanislav Fort state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. This allows a use-after-free race: CPU 0 CPU 1 ----- ----- state_show() damon_sysfs_turn_damon_on() ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); damon_destroy_ctx(kdamond->damon_ctx); kdamond->damon_ctx = NULL; mutex_unlock(&damon_sysfs_lock); damon_is_running(ctx); /* ctx is freed */ mutex_lock(&ctx->kdamond_lock); /* UAF */ (The race can also occur with damon_sysfs_kdamonds_rm_dirs() and damon_sysfs_kdamond_release(), which free or replace the context under damon_sysfs_lock.) Fix by taking damon_sysfs_lock before dereferencing the context, mirroring the locking used in pid_show(). The bug has existed since state_show() first accessed kdamond->damon_ctx. Link: https://lkml.kernel.org/r/20250905101046.2288-1-disclosure@aisle.com Fixes: a61ea561c871 ("mm/damon/sysfs: link DAMON for virtual address spaces monitoring") Signed-off-by: Stanislav Fort Reported-by: Stanislav Fort Reviewed-by: SeongJae Park Cc: Signed-off-by: Andrew Morton (cherry picked from commit 3260a3f0828e06f5f13fac69fb1999a6d60d9cff) Signed-off-by: SeongJae Park --- mm/damon/sysfs.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index b317f51dcc98..91893543d47c 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1055,14 +1055,18 @@ static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr, { struct damon_sysfs_kdamond *kdamond = container_of(kobj, struct damon_sysfs_kdamond, kobj); - struct damon_ctx *ctx = kdamond->damon_ctx; - bool running; + struct damon_ctx *ctx; + bool running = false; - if (!ctx) - running = false; - else + if (!mutex_trylock(&damon_sysfs_lock)) + return -EBUSY; + + ctx = kdamond->damon_ctx; + if (ctx) running = damon_sysfs_ctx_running(ctx); + mutex_unlock(&damon_sysfs_lock); + return sysfs_emit(buf, "%s\n", running ? damon_sysfs_cmd_strs[DAMON_SYSFS_CMD_ON] : damon_sysfs_cmd_strs[DAMON_SYSFS_CMD_OFF]); -- 2.39.5