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 A515B515967; Wed, 30 Sep 2026 16:07:28 +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=1790784453; cv=none; b=hTq8TwksA2452cXXv8xjKSfTKuSdhLUwPd2uBnENEj/aOcpKxa2J9WN5KCkpplGg/dmcscJf9hkTQtqI8dLU3NpYPHCbt3AdfAgcV+yf6U5XfuAdltyRuzm94zvLTH4FFN0UeunnmarPLjv3LZnwRm8ylcT68hwwMRgYRxMaswE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790784453; c=relaxed/simple; bh=eNsJV5gxkyuLH1MCqUjdevFOvRjIywXkjeMKeuERCFA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lgS415WuvLeL3BgqcBf1doKqOxuiMGYUxhErRiS/0k4+XtUeIr98V4nBP1RzJP7+7prhdE76FMZIO21WKvEayEMDt7Q+HEcwXUk1ojb0IuV5oKmyccNNOuJrH5NAkVN3XYjhOlBi2ihAG2y80o2AVXLM5LiprpcEFVRJD8KD4Is= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=edTtfG0d; 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="edTtfG0d" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BB99A1F00898; Wed, 30 Sep 2026 16:07:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790784448; bh=qPMe8e2g5nSM1+8EFxNFBpEZf0OxLeEEH0RoC25+YtQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=edTtfG0dtuTod8ysvXx+jxCcsx5d2xE3rCkFnOhbd1bsRrUQ4V4zQ1GI6QSNhqFCK /66P2BkIkJSdl7gUVD8cz7XDo+AAKKmK3mw42jr5qQ7qdbH6FbNpQcCgM51GsdoCbZ 563nRpTtFV1hBFzNYvazxSdG99c4Ms+PCAPlNz5Q= 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 6.1 157/982] bpf: NUL-terminate replaced sysctl value Date: Wed, 30 Sep 2026 17:14:53 +0200 Message-ID: <20260930152420.182844786@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152416.775402466@linuxfoundation.org> References: <20260930152416.775402466@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 6.1-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 3929c7548e6ff..6158b021f617f 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -2148,6 +2148,7 @@ 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