From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 B14E751814D; Thu, 17 Sep 2026 16:59:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789664396; cv=none; b=qgehXFRlQQbyBftfgf5Ht4txawOq7p0e4v62VJnPR+/iNiklrqytfDnRhlDJLlkuFmGuOxtbSKDXiPGUuIYt5t/ES1f6qEk0ln5RsBgRuWY/ulPQqKi99DbBSmn+BONEv7YPY6Ef6fQ9aDe9RTETtNPisW3bNWiCJYZcG0VNt9g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789664396; c=relaxed/simple; bh=GoDuk76zp3xQfXW5fwOEbEVWFUFVNDOwD0fAtbZlswI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YOoUpl8MjLrvsTHFNjC5AJlms9xraawNsurxAAlAdND/45A0p+0mm3dRPR6L43ZJ8thXTMsd5SmVPFXmkRLmGwYzGYhbj/QFkb5qlGapG2PyfBPoUcKRH85HlsXYd9x1PjiuwsnDcv9Qb0LchT3NZ+BcRJmSeT2AZXExQT+HYdM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Dn27+cKk; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Dn27+cKk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0142D1F00898; Thu, 17 Sep 2026 16:59:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789664395; bh=yjuycFMOs66a6jMJycgc6kewkb1a/AFXO+f7p+mOwRI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Dn27+cKk44K/GYiCNlrL31sdQZUIzpaW/hTA9F4zFqQE8OJV5xWlYDM2AY9mEKOrw r/SmjQtAszm3qtGXvN3JrZ/+V461xdt7DLomUR47dITs0ZCKn98pK/RfLDigDSJUcK Qa0hzZJP8WpVxeKdqUJc4f8pqrglrk4q63b6iCgI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Zilin Guan , Dawei Feng , Yonghong Song , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.18 0342/1250] bpf: NUL-terminate replaced sysctl value Date: Thu, 17 Sep 2026 16:02:17 +0100 Message-ID: <20260917151601.348923731@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151551.901433442@linuxfoundation.org> References: <20260917151551.901433442@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dawei Feng [ Upstream commit a66e3b5bacf38d6ab29fa05a9754f7a114485605 ] When writing to sysctls, proc_sys_call_handler() guarantees that the buffer passed to proc handlers is NUL-terminated. If bpf_sysctl_set_new_value() replaces the pending sysctl value, it can hand a replacement buffer directly to proc handlers. However, the helper currently copies only buf_len bytes into that buffer without appending a NUL terminator, leaving downstream parsers vulnerable to out-of-bounds access. Fix this by appending a '\0' after the replaced value to restore the expected sysctl semantics. Since the helper already rejects buf_len greater than PAGE_SIZE - 1, there is always room for the extra byte. Reproduced in a QEMU x86_64 guest booted with KASAN while exercising the sysctl replacement path with a cgroup/sysctl BPF program. The reproducer targets `/proc/sys/net/core/flow_limit_cpu_bitmap`, fills the original user write buffer with non-zero bytes, and overrides the sysctl value so the replacement buffer lacks a terminating NUL. Under that setup, the pre-fix kernel reported: BUG: KASAN: slab-out-of-bounds in strnchrnul+0x72/0x90 Read of size 1 at addr ffff88800de57000 by task repro_patch3/66 CPU: 0 UID: 0 PID: 66 Comm: repro_patch3 Not tainted 7.1.0-rc3-00269-g8370ca1f87cc #6 PREEMPT(lazy) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 Call Trace: dump_stack_lvl+0x68/0xa0 print_report+0xcb/0x5e0 ? __virt_addr_valid+0x21d/0x3f0 ? strnchrnul+0x72/0x90 ? strnchrnul+0x72/0x90 kasan_report+0xca/0x100 ? strnchrnul+0x72/0x90 strnchrnul+0x72/0x90 bitmap_parse+0x37/0x2e0 flow_limit_cpu_sysctl+0xc6/0x840 ? __pfx_flow_limit_cpu_sysctl+0x10/0x10 ? __kvmalloc_node_noprof+0x5ba/0x870 proc_sys_call_handler+0x31d/0x480 ? __pfx_proc_sys_call_handler+0x10/0x10 ? selinux_file_permission+0x39f/0x500 ? lock_is_held_type+0x9e/0x120 vfs_write+0x98e/0x1000 ... The buggy address is located 0 bytes to the right of allocated 4096-byte region [ffff88800de56000, ffff88800de57000) With this fix applied, rerunning the same sysctl-targeted path yields no corresponding KASAN reports. Signed-off-by: Zilin Guan Signed-off-by: Dawei Feng Acked-by: Yonghong Song Link: https://lore.kernel.org/r/20260603105317.944304-2-dawei.feng@seu.edu.cn Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/cgroup.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 8980373c7dab0..c652ba01bc8bd 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -2409,6 +2409,7 @@ BPF_CALL_3(bpf_sysctl_set_new_value, struct bpf_sysctl_kern *, ctx, return -E2BIG; memcpy(ctx->new_val, buf, buf_len); + ((char *)ctx->new_val)[buf_len] = '\0'; ctx->new_len = buf_len; ctx->new_updated = 1; -- 2.53.0