| Message ID | 20220722022416.137548-7-mfo@canonical.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Introduce "sysctl:" module aliases | expand |
On Fri, Jul 22, 2022 at 11:24 AM Mauricio Faria de Oliveira <mfo@canonical.com> wrote: > > The goal of the earlier patches is to let sysctl userspace tools > load the kernel module with a sysctl entry that is not available > yet in /proc/sys/ when the tool runs (so it can become available). > > Let's expose this file for userspace for two reasons: > > 1) Allow such tools to identify that the running kernel has the > code which produces sysctl module aliases, so they could run > 'modprobe sysctl:<entry>' only when it may actually help. > > 2) Allow an administrator to hint such tools not to do that, if > that is desired for some reason (e.g., rather have the tools > fail if something is misconfigured in a critical deployment). This flag is just a hint. User-space tools are still able to ignore it. Perhaps, such administrator's choice might be specified in tools' configuration file. For example, /etc/modprobe.d/forbid-sysctl-alias.conf may specify blacklist: sysctl:* if they want to forbid sysctl aliasing. (but I do not know if this works or not). > Also add a module parameter for that (proc.modprobe_sysctl_alias), > for another method that doesn't depend on sysctl tools to be set > (that wouldn't fail them to try and set it if it's not there yet). > > Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com> > --- > fs/proc/proc_sysctl.c | 8 ++++++++ > include/linux/module.h | 1 + > kernel/sysctl.c | 9 +++++++++ > 3 files changed, 18 insertions(+) > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c > index ebbf8702387e..1e63819fcda8 100644 > --- a/fs/proc/proc_sysctl.c > +++ b/fs/proc/proc_sysctl.c > @@ -33,6 +33,14 @@ static void check_struct_sysctl_device_id(void) > BUILD_BUG_ON(offsetof(struct sysctl_device_id, procname) > != offsetof(struct ctl_table, procname)); > } > + > +/* > + * Hint sysctl userspace tools whether or not to run modprobe with sysctl alias > + * ('modprobe sysctl:entry') if they cannot find the file '/proc/sys/.../entry' > + */ > +int modprobe_sysctl_alias = 1; > +module_param(modprobe_sysctl_alias, int, 0644); > + > #else > static void check_struct_sysctl_device_id(void) {} > #endif > diff --git a/include/linux/module.h b/include/linux/module.h > index 3010f687df19..5f565491c596 100644 > --- a/include/linux/module.h > +++ b/include/linux/module.h > @@ -304,6 +304,7 @@ struct notifier_block; > #ifdef CONFIG_MODULES > > extern int modules_disabled; /* for sysctl */ > +extern int modprobe_sysctl_alias; /* for proc sysctl */ > /* Get/put a kernel symbol (calls must be symmetric) */ > void *__symbol_get(const char *symbol); > void *__symbol_get_gpl(const char *symbol); > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 15073621cfa8..b396cfcb55fc 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1763,6 +1763,15 @@ static struct ctl_table kern_table[] = { > .mode = 0644, > .proc_handler = proc_dostring, > }, > +#ifdef CONFIG_PROC_SYSCTL > + { > + .procname = "modprobe_sysctl_alias", > + .data = &modprobe_sysctl_alias, > + .maxlen = sizeof(modprobe_sysctl_alias), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > +#endif > { > .procname = "modules_disabled", > .data = &modules_disabled, > -- > 2.25.1 > -- Best Regards Masahiro Yamada
On Tue, Jul 26, 2022 at 6:24 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > On Fri, Jul 22, 2022 at 11:24 AM Mauricio Faria de Oliveira > <mfo@canonical.com> wrote: > > > > The goal of the earlier patches is to let sysctl userspace tools > > load the kernel module with a sysctl entry that is not available > > yet in /proc/sys/ when the tool runs (so it can become available). > > > > Let's expose this file for userspace for two reasons: > > > > 1) Allow such tools to identify that the running kernel has the > > code which produces sysctl module aliases, so they could run > > 'modprobe sysctl:<entry>' only when it may actually help. > > > > 2) Allow an administrator to hint such tools not to do that, if > > that is desired for some reason (e.g., rather have the tools > > fail if something is misconfigured in a critical deployment). > > This flag is just a hint. > User-space tools are still able to ignore it. > > Perhaps, such administrator's choice might be specified in > tools' configuration file. > > For example, > > /etc/modprobe.d/forbid-sysctl-alias.conf > > may specify > > blacklist: sysctl:* > > if they want to forbid sysctl aliasing. > (but I do not know if this works or not). Yes, it's just a hint. I considered this isn't strong enough, but didn't think more into it. Now, your idea with modprobe.d is strong enough. We have to change it a bit, as only 'alias' supports wildcards per modprobe.d(5), then add 'install' to make sure. # cat /etc/modprobe.d/disable-sysctl-alias.conf alias sysctl:* sysctl_alias_off install sysctl_alias_off /bin/false # or /bin/true, per the sysadmin. # modprobe sysctl:nf_conntrack_max modprobe: ERROR: ../libkmod/libkmod-module.c:990 command_do() Error running install command '/bin/false' for module sysctl_alias_off: retcode 1 modprobe: ERROR: could not insert 'sysctl_alias_off': Invalid argument I'll document this in the commit message for now. P.S.: Since the flag is a hint to userspace tools in sense 1) as well (so they know not to run modprobe if sysctl aliases aren't expected), the idea or the file itself seems worth keeping -- but maybe differently. Thanks, > > > > > > > > > > > > > > > > Also add a module parameter for that (proc.modprobe_sysctl_alias), > > for another method that doesn't depend on sysctl tools to be set > > (that wouldn't fail them to try and set it if it's not there yet). > > > > Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com> > > --- > > fs/proc/proc_sysctl.c | 8 ++++++++ > > include/linux/module.h | 1 + > > kernel/sysctl.c | 9 +++++++++ > > 3 files changed, 18 insertions(+) > > > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c > > index ebbf8702387e..1e63819fcda8 100644 > > --- a/fs/proc/proc_sysctl.c > > +++ b/fs/proc/proc_sysctl.c > > @@ -33,6 +33,14 @@ static void check_struct_sysctl_device_id(void) > > BUILD_BUG_ON(offsetof(struct sysctl_device_id, procname) > > != offsetof(struct ctl_table, procname)); > > } > > + > > +/* > > + * Hint sysctl userspace tools whether or not to run modprobe with sysctl alias > > + * ('modprobe sysctl:entry') if they cannot find the file '/proc/sys/.../entry' > > + */ > > +int modprobe_sysctl_alias = 1; > > +module_param(modprobe_sysctl_alias, int, 0644); > > + > > #else > > static void check_struct_sysctl_device_id(void) {} > > #endif > > diff --git a/include/linux/module.h b/include/linux/module.h > > index 3010f687df19..5f565491c596 100644 > > --- a/include/linux/module.h > > +++ b/include/linux/module.h > > @@ -304,6 +304,7 @@ struct notifier_block; > > #ifdef CONFIG_MODULES > > > > extern int modules_disabled; /* for sysctl */ > > +extern int modprobe_sysctl_alias; /* for proc sysctl */ > > /* Get/put a kernel symbol (calls must be symmetric) */ > > void *__symbol_get(const char *symbol); > > void *__symbol_get_gpl(const char *symbol); > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > > index 15073621cfa8..b396cfcb55fc 100644 > > --- a/kernel/sysctl.c > > +++ b/kernel/sysctl.c > > @@ -1763,6 +1763,15 @@ static struct ctl_table kern_table[] = { > > .mode = 0644, > > .proc_handler = proc_dostring, > > }, > > +#ifdef CONFIG_PROC_SYSCTL > > + { > > + .procname = "modprobe_sysctl_alias", > > + .data = &modprobe_sysctl_alias, > > + .maxlen = sizeof(modprobe_sysctl_alias), > > + .mode = 0644, > > + .proc_handler = proc_dointvec, > > + }, > > +#endif > > { > > .procname = "modules_disabled", > > .data = &modules_disabled, > > -- > > 2.25.1 > > > > > -- > Best Regards > Masahiro Yamada -- Mauricio Faria de Oliveira
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index ebbf8702387e..1e63819fcda8 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -33,6 +33,14 @@ static void check_struct_sysctl_device_id(void) BUILD_BUG_ON(offsetof(struct sysctl_device_id, procname) != offsetof(struct ctl_table, procname)); } + +/* + * Hint sysctl userspace tools whether or not to run modprobe with sysctl alias + * ('modprobe sysctl:entry') if they cannot find the file '/proc/sys/.../entry' + */ +int modprobe_sysctl_alias = 1; +module_param(modprobe_sysctl_alias, int, 0644); + #else static void check_struct_sysctl_device_id(void) {} #endif diff --git a/include/linux/module.h b/include/linux/module.h index 3010f687df19..5f565491c596 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -304,6 +304,7 @@ struct notifier_block; #ifdef CONFIG_MODULES extern int modules_disabled; /* for sysctl */ +extern int modprobe_sysctl_alias; /* for proc sysctl */ /* Get/put a kernel symbol (calls must be symmetric) */ void *__symbol_get(const char *symbol); void *__symbol_get_gpl(const char *symbol); diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 15073621cfa8..b396cfcb55fc 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1763,6 +1763,15 @@ static struct ctl_table kern_table[] = { .mode = 0644, .proc_handler = proc_dostring, }, +#ifdef CONFIG_PROC_SYSCTL + { + .procname = "modprobe_sysctl_alias", + .data = &modprobe_sysctl_alias, + .maxlen = sizeof(modprobe_sysctl_alias), + .mode = 0644, + .proc_handler = proc_dointvec, + }, +#endif { .procname = "modules_disabled", .data = &modules_disabled,
The goal of the earlier patches is to let sysctl userspace tools load the kernel module with a sysctl entry that is not available yet in /proc/sys/ when the tool runs (so it can become available). Let's expose this file for userspace for two reasons: 1) Allow such tools to identify that the running kernel has the code which produces sysctl module aliases, so they could run 'modprobe sysctl:<entry>' only when it may actually help. 2) Allow an administrator to hint such tools not to do that, if that is desired for some reason (e.g., rather have the tools fail if something is misconfigured in a critical deployment). Also add a module parameter for that (proc.modprobe_sysctl_alias), for another method that doesn't depend on sysctl tools to be set (that wouldn't fail them to try and set it if it's not there yet). Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com> --- fs/proc/proc_sysctl.c | 8 ++++++++ include/linux/module.h | 1 + kernel/sysctl.c | 9 +++++++++ 3 files changed, 18 insertions(+)