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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id h15sm158986pfq.10.2020.03.25.15.42.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2020 15:42:23 -0700 (PDT) Date: Wed, 25 Mar 2020 15:42:22 -0700 From: Kees Cook To: Vlastimil Babka Cc: Luis Chamberlain , Iurii Zaikin , 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" Subject: Re: [RFC v2 2/2] kernel/sysctl: support handling command line aliases Message-ID: <202003251423.9138B8C8A9@keescook> References: <20200325120345.12946-1-vbabka@suse.cz> <20200325120345.12946-2-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200325120345.12946-2-vbabka@suse.cz> Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Mar 25, 2020 at 01:03:45PM +0100, Vlastimil Babka wrote: > We can now handle sysctl parameters on kernel command line, but historically > some parameters introduced their own command line equivalent, which we don't > want to remove for compatibility reasons. We can however convert them to the > generic infrastructure with a table translating the legacy command line > parameters to their sysctl names, and removing the one-off param handlers. > > This patch adds the support and makes the first conversion to demonstrate it, > on the (deprecated) numa_zonelist_order parameter. > > Signed-off-by: Vlastimil Babka > --- > kernel/sysctl.c | 39 +++++++++++++++++++++++++++++++++++---- > mm/page_alloc.c | 9 --------- > 2 files changed, 35 insertions(+), 13 deletions(-) > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 18c7f5606d55..fd72853396f9 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1971,6 +1971,22 @@ static struct ctl_table dev_table[] = { > { } > }; > > +struct sysctl_alias { > + char *kernel_param; const char ... > + char *sysctl_param; > +}; > + > +/* > + * Historically some settings had both sysctl and a command line parameter. > + * With the generic sysctl. parameter support, we can handle them at a single > + * place and only keep the historical name for compatibility. This is not meant > + * to add brand new aliases. > + */ > +static struct sysctl_alias sysctl_aliases[] = { static const ... > + {"numa_zonelist_order", "vm.numa_zonelist_order" }, > + { } > +}; > + > int __init sysctl_init(void) > { > struct ctl_table_header *hdr; > @@ -1980,6 +1996,18 @@ int __init sysctl_init(void) > return 0; > } > > +char *sysctl_find_alias(char *param) > +{ > + struct sysctl_alias *alias; > + > + for (alias = &sysctl_aliases[0]; alias->kernel_param != NULL; alias++) { > + if (strcmp(alias->kernel_param, param) == 0) > + return alias->sysctl_param; > + } > + > + return NULL; > +} > + > /* Set sysctl value passed on kernel command line. */ > int process_sysctl_arg(char *param, char *val, > const char *unused, void *arg) > @@ -1990,10 +2018,13 @@ int process_sysctl_arg(char *param, char *val, > loff_t ppos = 0; > struct ctl_table *ctl, *found = NULL; > > - if (strncmp(param, "sysctl.", sizeof("sysctl.") - 1)) > - return 0; > - > - param += sizeof("sysctl.") - 1; > + if (strncmp(param, "sysctl.", sizeof("sysctl.") - 1) == 0) { > + param += sizeof("sysctl.") - 1; > + } else { > + param = sysctl_find_alias(param); > + if (!param) > + return 0; > + } > > remaining = param; > ctl = &sysctl_base_table[0]; > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3c4eb750a199..de7a134b1b8a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5460,15 +5460,6 @@ static int __parse_numa_zonelist_order(char *s) > return 0; > } > > -static __init int setup_numa_zonelist_order(char *s) > -{ > - if (!s) > - return 0; > - > - return __parse_numa_zonelist_order(s); > -} > -early_param("numa_zonelist_order", setup_numa_zonelist_order); > - > char numa_zonelist_order[] = "Node"; Nice. :) Effectively: -9 lines +1 line for the using aliasing. I think it would be worth identifying the specific requirements for a sysctl alias to be safe to use, and likely in a comment before the alias table: - boot param parsing must be identical to the sysctl parsing - temporal changes must be tolerable: i.e. early_param() runs earlier than when the sysctl-in-boot-param runs -- must the variable be set before the code's other __init functions run? - must be for a non-module code (since we don't have the dynamic support yet) As it turns out, "numa_zonelist_order" has literally no effect on anything -- it's a parsed but ignored setting: static int __parse_numa_zonelist_order(char *s) { /* * We used to support different zonlists modes but they turned * out to be just not useful. Let's keep the warning in place * if somebody still use the cmd line parameter so that we do * not fail it silently */ if (!(*s == 'd' || *s == 'D' || *s == 'n' || *s == 'N')) { pr_warn("Ignoring unsupported numa_zonelist_order value: %s\n", s); return -EINVAL; } return 0; } But anyway, do you have a way to generate a list of potential candidates? -- Kees Cook