From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 798ABC81982 for ; Mon, 27 Apr 2020 18:05:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3922E206D4 for ; Mon, 27 Apr 2020 18:05:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3922E206D4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 83AA88E0009; Mon, 27 Apr 2020 14:04:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4CFD58E0006; Mon, 27 Apr 2020 14:04:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1EA508E0009; Mon, 27 Apr 2020 14:04:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0154.hostedemail.com [216.40.44.154]) by kanga.kvack.org (Postfix) with ESMTP id BCFF38E0009 for ; Mon, 27 Apr 2020 14:04:51 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 6D4D44FFA for ; Mon, 27 Apr 2020 18:04:51 +0000 (UTC) X-FDA: 76754410782.12.pin52_6489eab00fa45 X-HE-Tag: pin52_6489eab00fa45 X-Filterd-Recvd-Size: 9708 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf33.hostedemail.com (Postfix) with ESMTP for ; Mon, 27 Apr 2020 18:04:50 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id EAC1AABE2; Mon, 27 Apr 2020 18:04:47 +0000 (UTC) From: Vlastimil Babka To: Andrew Morton , Luis Chamberlain , Kees Cook , Iurii Zaikin Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, Ivan Teterevkov , Michal Hocko , David Rientjes , Matthew Wilcox , "Eric W . Biederman" , "Guilherme G . Piccoli" , Alexey Dobriyan , Thomas Gleixner , Greg Kroah-Hartman , Christian Brauner , Masami Hiramatsu , Vlastimil Babka , Michal Hocko Subject: [PATCH v3 1/5] kernel/sysctl: support setting sysctl parameters from kernel command line Date: Mon, 27 Apr 2020 20:04:29 +0200 Message-Id: <20200427180433.7029-2-vbabka@suse.cz> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200427180433.7029-1-vbabka@suse.cz> References: <20200427180433.7029-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: A recently proposed patch to add vm_swappiness command line parameter in addition to existing sysctl [1] made me wonder why we don't have a genera= l support for passing sysctl parameters via command line. Googling found on= ly somebody else wondering the same [2], but I haven't found any prior discu= ssion with reasons why not to do this. Settings the vm_swappiness issue aside (the underlying issue might be sol= ved in a different way), quick search of kernel-parameters.txt shows there are a= lready some that exist as both sysctl and kernel parameter - hung_task_panic, nmi_watchdog, numa_zonelist_order, traceoff_on_warning. A general mechani= sm would remove the need to add more of those one-offs and might be handy in situations where configuration by e.g. /etc/sysctl.d/ is impractical. Hence, this patch adds a new parse_args() pass that looks for parameters prefixed by 'sysctl.' and tries to interpret them as writes to the corresponding sys/ files using an temporary in-kernel procfs mount. This mechanism was suggested by Eric W. Biederman [3], as it handles all dynam= ically registered sysctl tables, even though we don't handle modular sysctls. Er= rors due to e.g. invalid parameter name or value are reported in the kernel lo= g. The processing is hooked right before the init process is loaded, as some handlers might be more complicated than simple setters and might need som= e subsystems to be initialized. At the moment the init process can be start= ed and eventually execute a process writing to /proc/sys/ then it should be also= fine to do that from the kernel. Sysctls registered later on module load time are not set by this mechanis= m - it's expected that in such scenarios, setting sysctl values from userspac= e is practical enough. [1] https://lore.kernel.org/r/BL0PR02MB560167492CA4094C91589930E9FC0@BL0P= R02MB5601.namprd02.prod.outlook.com/ [2] https://unix.stackexchange.com/questions/558802/how-to-set-sysctl-usi= ng-kernel-command-line-parameter [3] https://lore.kernel.org/r/87bloj2skm.fsf@x220.int.ebiederm.org/ Signed-off-by: Vlastimil Babka Reviewed-by: Luis Chamberlain Reviewed-by: Masami Hiramatsu Acked-by: Kees Cook Acked-by: Michal Hocko --- .../admin-guide/kernel-parameters.txt | 9 ++ fs/proc/proc_sysctl.c | 107 ++++++++++++++++++ include/linux/sysctl.h | 4 + init/main.c | 2 + 4 files changed, 122 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentat= ion/admin-guide/kernel-parameters.txt index 7bc83f3d9bdf..73dbbf942431 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4891,6 +4891,15 @@ =20 switches=3D [HW,M68k] =20 + sysctl.*=3D [KNL] + Set a sysctl parameter, right before loading the init + process, as if the value was written to the respective + /proc/sys/... file. Both '.' and '/' are recognized as + separators. Unrecognized parameters and invalid values + are reported in the kernel log. Sysctls registered + later by a loaded module cannot be set this way. + Example: sysctl.vm.swappiness=3D40 + sysfs.deprecated=3D0|1 [KNL] Enable/disable old style sysfs layout for old udev on older distributions. When this option is enabled diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index b6f5d459b087..7804da5f5be0 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -14,6 +14,7 @@ #include #include #include +#include #include "internal.h" =20 static const struct dentry_operations proc_sys_dentry_operations; @@ -1692,3 +1693,109 @@ int __init proc_sys_init(void) =20 return sysctl_init(); } + +/* Set sysctl value passed on kernel command line. */ +static int process_sysctl_arg(char *param, char *val, + const char *unused, void *arg) +{ + char *path; + struct vfsmount **proc_mnt =3D arg; + struct file_system_type *proc_fs_type; + struct file *file; + int len; + int err; + loff_t pos =3D 0; + ssize_t wret; + + if (strncmp(param, "sysctl", sizeof("sysctl") - 1)) + return 0; + + param +=3D sizeof("sysctl") - 1; + + if (param[0] !=3D '/' && param[0] !=3D '.') + return 0; + + param++; + + /* + * To set sysctl options, we use a temporary mount of proc, look up the + * respective sys/ file and write to it. To avoid mounting it when no + * options were given, we mount it only when the first sysctl option is + * found. Why not a persistent mount? There are problems with a + * persistent mount of proc in that it forces userspace not to use any + * proc mount options. + */ + if (!*proc_mnt) { + proc_fs_type =3D get_fs_type("proc"); + if (!proc_fs_type) { + pr_err("Failed to find procfs to set sysctl from command line\n"); + return 0; + } + *proc_mnt =3D kern_mount(proc_fs_type); + put_filesystem(proc_fs_type); + if (IS_ERR(*proc_mnt)) { + pr_err("Failed to mount procfs to set sysctl from command line\n"); + return 0; + } + } + + path =3D kasprintf(GFP_KERNEL, "sys/%s", param); + if (!path) + panic("%s: Failed to allocate path for %s\n", __func__, param); + strreplace(path, '.', '/'); + + file =3D file_open_root((*proc_mnt)->mnt_root, *proc_mnt, path, O_WRONL= Y, 0); + if (IS_ERR(file)) { + err =3D PTR_ERR(file); + if (err =3D=3D -ENOENT) + pr_err("Failed to set sysctl parameter '%s=3D%s': parameter not found= \n", + param, val); + else if (err =3D=3D -EACCES) + pr_err("Failed to set sysctl parameter '%s=3D%s': permission denied (= read-only?)\n", + param, val); + else + pr_err("Error %pe opening proc file to set sysctl parameter '%s=3D%s'= \n", + file, param, val); + goto out; + } + len =3D strlen(val); + wret =3D kernel_write(file, val, len, &pos); + if (wret < 0) { + err =3D wret; + if (err =3D=3D -EINVAL) + pr_err("Failed to set sysctl parameter '%s=3D%s': invalid value\n", + param, val); + else + pr_err("Error %pe writing to proc file to set sysctl parameter '%s=3D= %s'\n", + ERR_PTR(err), param, val); + } else if (wret !=3D len) { + pr_err("Wrote only %zd bytes of %d writing to proc file %s to set sysc= tl parameter '%s=3D%s\n", + wret, len, path, param, val); + } + + err =3D filp_close(file, NULL); + if (err) + pr_err("Error %pe closing proc file to set sysctl parameter '%s=3D%s\n= ", + ERR_PTR(err), param, val); +out: + kfree(path); + return 0; +} + +void do_sysctl_args(void) +{ + char *command_line; + struct vfsmount *proc_mnt =3D NULL; + + command_line =3D kstrdup(saved_command_line, GFP_KERNEL); + if (!command_line) + panic("%s: Failed to allocate copy of command line\n", __func__); + + parse_args("Setting sysctl args", command_line, + NULL, 0, -1, -1, &proc_mnt, process_sysctl_arg); + + if (proc_mnt) + kern_unmount(proc_mnt); + + kfree(command_line); +} diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index 02fa84493f23..bee62d30ebdb 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -206,6 +206,7 @@ struct ctl_table_header *register_sysctl_paths(const = struct ctl_path *path, void unregister_sysctl_table(struct ctl_table_header * table); =20 extern int sysctl_init(void); +void do_sysctl_args(void); =20 extern struct ctl_table sysctl_mount_point[]; =20 @@ -236,6 +237,9 @@ static inline void setup_sysctl_set(struct ctl_table_= set *p, { } =20 +static inline void do_sysctl_args(void) +{ +} #endif /* CONFIG_SYSCTL */ =20 int sysctl_max_threads(struct ctl_table *table, int write, diff --git a/init/main.c b/init/main.c index a48617f2e5e5..7b43118215d6 100644 --- a/init/main.c +++ b/init/main.c @@ -1372,6 +1372,8 @@ static int __ref kernel_init(void *unused) =20 rcu_end_inkernel_boot(); =20 + do_sysctl_args(); + if (ramdisk_execute_command) { ret =3D run_init_process(ramdisk_execute_command); if (!ret) --=20 2.26.0