From nobody Wed Nov 27 18:31:25 2024 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (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 260B9144D21 for ; Tue, 8 Oct 2024 15:15:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728400515; cv=none; b=CTHyR/5xk6vfYV5T9sjRDsOjwgzBWZDNpQFBLs/1MDs+WEI9IETZGpQih1NXs/a2eL/ic4aiQRNWOTAvss4abP6ZICl4zBrpdlVgyk3qzb+A0lb/jotmypc5wVTHQL7GKoA5MtU7hPl7ZBsP5437TpetZDjfDLCyPygmXXQL4EI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728400515; c=relaxed/simple; bh=Wnkw6FFBKsXGaqRKw8ABC0jfMs+Zrg/uyo0kDJCVi0A=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=kHfHAwUcLO9qh+h2zb3hzERoMJlHId3USJwQvc9kLqGlFSEltJf/axB7a3RO49Ll2k2ApbuQUvbARQkizeQNk6bI2o5op2HnCbLR8FyGfEYWW3yBQY6W+Fp22H6LoQOvAoC1vjQ/hZ0mCrWQjLzT9WnvdxFYgjLNAkjY7557rFc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=u4S00+YO; arc=none smtp.client-ip=95.215.58.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="u4S00+YO" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1728400511; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WKCitTbsUobcgrflXEj+ca1BYMZMbnrUxAHKkSj7J70=; b=u4S00+YOB7yWeg2TEp7pfcjTA0hU/ODQu1gQRfBS7xPBCtRPRfovi6dj3WdCx1uunyPIEv M+BRMG9yNIfDV6m3YoTjIMMuMh2lVZMEtqnN24/jYjiNLFOtD3jqnGSv8AhRuOm+veRVFo aFFo6GuNgI16Dc1/TtqfnMVziR6Fj5Q= From: Wen Yang To: Joel Granados , Luis Chamberlain , Kees Cook Cc: "Eric W . Biederman" , Christian Brauner , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= , linux-kernel@vger.kernel.org, Wen Yang , Dave Young Subject: [RESEND PATCH v4 2/5] sysctl: support encoding values directly in the table entry Date: Tue, 8 Oct 2024 23:14:05 +0800 Message-Id: <20241008151444.12453-2-wen.yang@linux.dev> In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" Eric points out: "by turning .extra1 and .extra2 into longs instead of keeping them as pointers and needing constants to be pointed at somewhere .. The only people I can see who find a significant benefit by consolidating all of the constants into one place are people who know how to stomp kernel memory." This patch supports encoding values directly in table entries through the following work: - extra1/extra2 and min/max are placed in one union to ensure compatibility with previous code without increasing memory overhead, and then we could gradually remove these unnecessary extra1/extra2. - two bits were used to represent the information of the above union: SYSCTL_FLAG_MIN: 0, using extra1. 1, using min. SYSCTL_FLAG_MAX: 0, using extra2. 1, using max. - since the proc file's mode field only uses 9 bits(777), we could use the additional two bits(S_ISUID and S_ISGID) to temporarily represent SYSCTL_FLAG_MIN and SYSCTL_FLAG_MAX. - added some helper macros. By introducing long min/max to replace void * extra1/extra2 in most cases, unnecessary variables can be removed to save memory and avoid attacks. Signed-off-by: Wen Yang Cc: Luis Chamberlain Cc: Kees Cook Cc: Joel Granados Cc: Eric W. Biederman Cc: Christian Brauner Cc: Dave Young Cc: linux-kernel@vger.kernel.org --- fs/proc/proc_sysctl.c | 8 ++++++-- include/linux/sysctl.h | 24 ++++++++++++++++++++---- 2 files changed, 26 insertions(+), 6 deletions(-) diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index 90c99eb1abf6..e88d1dca2a80 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -848,8 +848,11 @@ static int proc_sys_getattr(struct mnt_idmap *idmap, return PTR_ERR(head); =20 generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat); - if (table) + if (table) { stat->mode =3D (stat->mode & S_IFMT) | table->mode; + stat->mode &=3D ~SYSCTL_FLAG_MIN; + stat->mode &=3D ~SYSCTL_FLAG_MAX; + } =20 sysctl_head_finish(head); return 0; @@ -1163,7 +1166,8 @@ static int sysctl_check_table(const char *path, struc= t ctl_table_header *header) if (!entry->proc_handler) err |=3D sysctl_err(path, entry, "No proc_handler"); =20 - if ((entry->mode & (S_IRUGO|S_IWUGO)) !=3D entry->mode) + if ((entry->mode & (S_IRUGO|S_IWUGO|SYSCTL_FLAG_MIN|SYSCTL_FLAG_MAX)) + !=3D entry->mode) err |=3D sysctl_err(path, entry, "bogus .mode 0%o", entry->mode); } diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index edfcb22b1e3d..859b016aa76e 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -28,6 +28,7 @@ #include #include #include +#include =20 /* For the /proc/sys support */ struct completion; @@ -131,6 +132,9 @@ static inline void *proc_sys_poll_event(struct ctl_tabl= e_poll *poll) #define DEFINE_CTL_TABLE_POLL(name) \ struct ctl_table_poll name =3D __CTL_TABLE_POLL_INITIALIZER(name) =20 +#define SYSCTL_FLAG_MIN S_ISUID +#define SYSCTL_FLAG_MAX S_ISGID + /* A sysctl table is an array of struct ctl_table: */ struct ctl_table { const char *procname; /* Text ID for /proc/sys, or zero */ @@ -139,8 +143,16 @@ struct ctl_table { umode_t mode; proc_handler *proc_handler; /* Callback for text formatting */ struct ctl_table_poll *poll; - void *extra1; - void *extra2; + union { + struct { + void *extra1; + void *extra2; + }; + struct { + long min; + long max; + }; + }; } __randomize_layout; =20 struct ctl_node { @@ -212,9 +224,13 @@ struct ctl_table_root { #define register_sysctl(path, table) \ register_sysctl_sz(path, table, ARRAY_SIZE(table)) =20 -#define __SYSCTL_RANGE_MIN(_a, _b, _c) (((_a)->extra1) ? *(_b((_a)->extra1= )) : (_c)) +#define __SYSCTL_RANGE_EXTRA1(_a, _b, _c) (((_a)->extra1) ? *(_b((_a)->ext= ra1)) : (_c)) +#define __SYSCTL_RANGE_MIN(_a, _b, _c) ((((_a)->mode) & SYSCTL_FLAG_MIN= ) ? \ + ((_a)->min) : __SYSCTL_RANGE_EXTRA1(_a, _b, _c)) =20 -#define __SYSCTL_RANGE_MAX(_a, _b, _c) (((_a)->extra2) ? *(_b((_a)->extra2= )) : (_c)) +#define __SYSCTL_RANGE_EXTRA2(_a, _b, _c) (((_a)->extra2) ? *(_b((_a)->ext= ra2)) : (_c)) +#define __SYSCTL_RANGE_MAX(_a, _b, _c) ((((_a)->mode) & SYSCTL_FLAG_MAX= ) ? \ + ((_a)->max) : __SYSCTL_RANGE_EXTRA2(_a, _b, _c)) =20 static inline unsigned int sysctl_range_min_u8(const struct ctl_table *tab= le) { --=20 2.25.1