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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 8A45DC2D0ED for ; Thu, 26 Mar 2020 18:16:27 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4CF422073E for ; Thu, 26 Mar 2020 18:16:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4CF422073E 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 1148A6B000C; Thu, 26 Mar 2020 14:16:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 09DF86B0010; Thu, 26 Mar 2020 14:16:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EA7496B0032; Thu, 26 Mar 2020 14:16:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0167.hostedemail.com [216.40.44.167]) by kanga.kvack.org (Postfix) with ESMTP id B0FBE6B000C for ; Thu, 26 Mar 2020 14:16:25 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id D6377180ACEE4 for ; Thu, 26 Mar 2020 18:16:25 +0000 (UTC) X-FDA: 76638318330.17.cars37_552f2a5371449 X-HE-Tag: cars37_552f2a5371449 X-Filterd-Recvd-Size: 8628 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Thu, 26 Mar 2020 18:16:25 +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 D7CC6ADDA; Thu, 26 Mar 2020 18:16:22 +0000 (UTC) From: Vlastimil Babka To: 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" , Vlastimil Babka Subject: [RFC v3 1/2] kernel/sysctl: support setting sysctl parameters from kernel command line Date: Thu, 26 Mar 2020 19:16:05 +0100 Message-Id: <20200326181606.7027-1-vbabka@suse.cz> X-Mailer: git-send-email 2.25.1 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. Errors due to e.g. invalid parameter name or va= lue are reported in the kernel log. 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 --- Changes in v3: - use temporary procfs mount as Eric suggested. Seems to be the better op= tion after all. Naming wise it simply converts all . to / - according to str= ace the sysctl tool seems to be doing the same. Since the major change, I'm sending another RFC. If this approach is ok, = then it probably needs just some tweaks to the various error prints, and then converting the rest of existing on-off aliases (if I come up with an idea= how to find them all). Thanks for all the feedback so far. .../admin-guide/kernel-parameters.txt | 9 ++ fs/proc/proc_sysctl.c | 90 +++++++++++++++++++ include/linux/sysctl.h | 4 + init/main.c | 2 + 4 files changed, 105 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentat= ion/admin-guide/kernel-parameters.txt index c07815d230bc..0c7e032e7c2e 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4793,6 +4793,15 @@ =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. 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 c75bb4632ed1..8ee3273e4540 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; @@ -1725,3 +1726,92 @@ int __init proc_sys_init(void) =20 return sysctl_init(); } + +struct vfsmount *proc_mnt =3D NULL; + +/* 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 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++; + + if (!proc_mnt) { + proc_fs_type =3D get_fs_type("proc"); + if (!proc_fs_type) { + pr_err("Failed to mount procfs to set sysctl from command line"); + 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"); + proc_mnt =3D NULL; + return 0; + } + } + + len =3D 4 + strlen(param) + 1; + path =3D kmalloc(len, GFP_KERNEL); + if (!path) + panic("%s: Failed to allocate %d bytes t\n", __func__, len); + + strcpy(path, "sys/"); + strcat(path, param); + strreplace(path, '.', '/'); + + file =3D file_open_root(proc_mnt->mnt_root, proc_mnt, path, O_WRONLY, 0= ); + if (IS_ERR(file)) { + err =3D PTR_ERR(file); + pr_err("Error %d opening proc file %s to set sysctl parameter '%s=3D%s= '", + err, path, param, val); + goto out; + } + len =3D strlen(val); + wret =3D kernel_write(file, val, len, &pos); + if (wret < 0) { + err =3D wret; + pr_err("Error %d writing to proc file %s to set sysctl parameter '%s=3D= %s'", + err, path, param, val); + } else if (wret !=3D len) { + pr_err("Wrote only %ld bytes of %d writing to proc file %s to set sys= ctl parameter '%s=3D%s'", + wret, len, path, param, val); + } + + filp_close(file, NULL); +out: + kfree(path); + return 0; +} + +void do_sysctl_args(void) +{ + char *command_line; + + 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, NULL, 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..5f3f2a00d75f 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 +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 ee4947af823f..a91ea166a731 100644 --- a/init/main.c +++ b/init/main.c @@ -1367,6 +1367,8 @@ 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 2.25.1