2022-06-16 17:47:48

by Micah Morton

Subject: [PATCH 1/3] security: Add LSM hook to setgroups() syscall

Give the LSM framework the ability to filter setgroups() syscalls. There
are already analagous hooks for the set*uid() and set*gid() syscalls.
The SafeSetID LSM will use this new hook to ensure setgroups() calls are
allowed by the installed security policy. Tested by putting print
statement in security_task_fix_setgroups() hook and confirming that it
gets hit when userspace does a setgroups() syscall.

Signed-off-by: Micah Morton <[email protected]>
---
include/linux/lsm_hook_defs.h | 1 +
include/linux/lsm_hooks.h | 7 +++++++
include/linux/security.h | 7 +++++++
kernel/groups.c | 13 +++++++++++++
security/security.c | 5 +++++
5 files changed, 33 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index eafa1d2489fd..806448173033 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -201,6 +201,7 @@ LSM_HOOK(int, 0, task_fix_setuid, struct cred *new, const struct cred *old,
int flags)
LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old,
int flags)
+LSM_HOOK(int, 0, task_fix_setgroups, struct cred *new, const struct cred * old)
LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid)
LSM_HOOK(int, 0, task_getpgid, struct task_struct *p)
LSM_HOOK(int, 0, task_getsid, struct task_struct *p)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 91c8146649f5..84a0d7e02176 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -702,6 +702,13 @@
* @old is the set of credentials that are being replaced.
* @flags contains one of the LSM_SETID_* values.
* Return 0 on success.
+ * @task_fix_setgroups:
+ * Update the module's state after setting the supplementary group
+ * identity attributes of the current process.
+ * @new is the set of credentials that will be installed. Modifications
+ * should be made to this rather than to @current->cred.
+ * @old is the set of credentials that are being replaced.
+ * Return 0 on success.
* @task_setpgid:
* Check permission before setting the process group identifier of the
* process @p to @pgid.
diff --git a/include/linux/security.h b/include/linux/security.h
index 7fc4e9f49f54..1dfd32c49fa3 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -415,6 +415,7 @@ int security_task_fix_setuid(struct cred *new, const struct cred *old,
int flags);
int security_task_fix_setgid(struct cred *new, const struct cred *old,
int flags);
+int security_task_fix_setgroups(struct cred *new, const struct cred *old);
int security_task_setpgid(struct task_struct *p, pid_t pgid);
int security_task_getpgid(struct task_struct *p);
int security_task_getsid(struct task_struct *p);
@@ -1098,6 +1099,12 @@ static inline int security_task_fix_setgid(struct cred *new,
return 0;
}

+static inline int security_task_fix_setgroups(struct cred *new,
+ const struct cred *old)
+{
+ return 0;
+}
+
static inline int security_task_setpgid(struct task_struct *p, pid_t pgid)
{
return 0;
diff --git a/kernel/groups.c b/kernel/groups.c
index 787b381c7c00..9aaed2a31073 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -134,13 +134,26 @@ EXPORT_SYMBOL(set_groups);
int set_current_groups(struct group_info *group_info)
{
struct cred *new;
+ const struct cred *old;
+ int retval;

new = prepare_creds();
if (!new)
return -ENOMEM;

+ old = current_cred();
+
set_groups(new, group_info);
+
+ retval = security_task_fix_setgroups(new, old);
+ if (retval < 0)
+ goto error;
+
return commit_creds(new);
+
+error:
+ abort_creds(new);
+ return retval;
}

EXPORT_SYMBOL(set_current_groups);
diff --git a/security/security.c b/security/security.c
index 188b8f782220..15c686145ad6 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1803,6 +1803,11 @@ int security_task_fix_setgid(struct cred *new, const struct cred *old,
return call_int_hook(task_fix_setgid, 0, new, old, flags);
}

+int security_task_fix_setgroups(struct cred *new, const struct cred *old)
+{
+ return call_int_hook(task_fix_setgroups, 0, new, old);
+}
+
int security_task_setpgid(struct task_struct *p, pid_t pgid)
{
return call_int_hook(task_setpgid, 0, p, pgid);
--
2.36.1.476.g0c4daa206d-goog

2022-06-20 18:41:33

by Casey Schaufler

Subject: Re: [PATCH 1/3] security: Add LSM hook to setgroups() syscall

On 6/16/2022 10:18 AM, Micah Morton wrote:
> Give the LSM framework the ability to filter setgroups() syscalls. There
> are already analagous hooks for the set*uid() and set*gid() syscalls.
> The SafeSetID LSM will use this new hook to ensure setgroups() calls are
> allowed by the installed security policy. Tested by putting print
> statement in security_task_fix_setgroups() hook and confirming that it
> gets hit when userspace does a setgroups() syscall.
>
> Signed-off-by: Micah Morton <[email protected]>

I don't see any problems with this.
Acked-by: Casey Schaufler <[email protected]>

> ---
> include/linux/lsm_hook_defs.h | 1 +
> include/linux/lsm_hooks.h | 7 +++++++
> include/linux/security.h | 7 +++++++
> kernel/groups.c | 13 +++++++++++++
> security/security.c | 5 +++++
> 5 files changed, 33 insertions(+)
>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index eafa1d2489fd..806448173033 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -201,6 +201,7 @@ LSM_HOOK(int, 0, task_fix_setuid, struct cred *new, const struct cred *old,
> int flags)
> LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old,
> int flags)
> +LSM_HOOK(int, 0, task_fix_setgroups, struct cred *new, const struct cred * old)
> LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid)
> LSM_HOOK(int, 0, task_getpgid, struct task_struct *p)
> LSM_HOOK(int, 0, task_getsid, struct task_struct *p)
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 91c8146649f5..84a0d7e02176 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -702,6 +702,13 @@
> * @old is the set of credentials that are being replaced.
> * @flags contains one of the LSM_SETID_* values.
> * Return 0 on success.
> + * @task_fix_setgroups:
> + * Update the module's state after setting the supplementary group
> + * identity attributes of the current process.
> + * @new is the set of credentials that will be installed. Modifications
> + * should be made to this rather than to @current->cred.
> + * @old is the set of credentials that are being replaced.
> + * Return 0 on success.
> * @task_setpgid:
> * Check permission before setting the process group identifier of the
> * process @p to @pgid.
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 7fc4e9f49f54..1dfd32c49fa3 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -415,6 +415,7 @@ int security_task_fix_setuid(struct cred *new, const struct cred *old,
> int flags);
> int security_task_fix_setgid(struct cred *new, const struct cred *old,
> int flags);
> +int security_task_fix_setgroups(struct cred *new, const struct cred *old);
> int security_task_setpgid(struct task_struct *p, pid_t pgid);
> int security_task_getpgid(struct task_struct *p);
> int security_task_getsid(struct task_struct *p);
> @@ -1098,6 +1099,12 @@ static inline int security_task_fix_setgid(struct cred *new,
> return 0;
> }
>
> +static inline int security_task_fix_setgroups(struct cred *new,
> + const struct cred *old)
> +{
> + return 0;
> +}
> +
> static inline int security_task_setpgid(struct task_struct *p, pid_t pgid)
> {
> return 0;
> diff --git a/kernel/groups.c b/kernel/groups.c
> index 787b381c7c00..9aaed2a31073 100644
> --- a/kernel/groups.c
> +++ b/kernel/groups.c
> @@ -134,13 +134,26 @@ EXPORT_SYMBOL(set_groups);
> int set_current_groups(struct group_info *group_info)
> {
> struct cred *new;
> + const struct cred *old;
> + int retval;
>
> new = prepare_creds();
> if (!new)
> return -ENOMEM;
>
> + old = current_cred();
> +
> set_groups(new, group_info);
> +
> + retval = security_task_fix_setgroups(new, old);
> + if (retval < 0)
> + goto error;
> +
> return commit_creds(new);
> +
> +error:
> + abort_creds(new);
> + return retval;
> }
>
> EXPORT_SYMBOL(set_current_groups);
> diff --git a/security/security.c b/security/security.c
> index 188b8f782220..15c686145ad6 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1803,6 +1803,11 @@ int security_task_fix_setgid(struct cred *new, const struct cred *old,
> return call_int_hook(task_fix_setgid, 0, new, old, flags);
> }
>
> +int security_task_fix_setgroups(struct cred *new, const struct cred *old)
> +{
> + return call_int_hook(task_fix_setgroups, 0, new, old);
> +}
> +
> int security_task_setpgid(struct task_struct *p, pid_t pgid)
> {
> return call_int_hook(task_setpgid, 0, p, pgid);

2022-06-27 00:18:57

by Serge E. Hallyn

Subject: Re: [PATCH 1/3] security: Add LSM hook to setgroups() syscall

On Mon, Jun 20, 2022 at 11:15:05AM -0700, Casey Schaufler wrote:
> On 6/16/2022 10:18 AM, Micah Morton wrote:
> > Give the LSM framework the ability to filter setgroups() syscalls. There
> > are already analagous hooks for the set*uid() and set*gid() syscalls.
> > The SafeSetID LSM will use this new hook to ensure setgroups() calls are
> > allowed by the installed security policy. Tested by putting print
> > statement in security_task_fix_setgroups() hook and confirming that it
> > gets hit when userspace does a setgroups() syscall.
> >
> > Signed-off-by: Micah Morton <[email protected]>
>
> I don't see any problems with this.
> Acked-by: Casey Schaufler <[email protected]>
>

Ditto. Thanks.

Reviewed-by: Serge Hallyn <[email protected]>

> > ---
> > include/linux/lsm_hook_defs.h | 1 +
> > include/linux/lsm_hooks.h | 7 +++++++
> > include/linux/security.h | 7 +++++++
> > kernel/groups.c | 13 +++++++++++++
> > security/security.c | 5 +++++
> > 5 files changed, 33 insertions(+)
> >
> > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> > index eafa1d2489fd..806448173033 100644
> > --- a/include/linux/lsm_hook_defs.h
> > +++ b/include/linux/lsm_hook_defs.h
> > @@ -201,6 +201,7 @@ LSM_HOOK(int, 0, task_fix_setuid, struct cred *new, const struct cred *old,
> > int flags)
> > LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old,
> > int flags)
> > +LSM_HOOK(int, 0, task_fix_setgroups, struct cred *new, const struct cred * old)
> > LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid)
> > LSM_HOOK(int, 0, task_getpgid, struct task_struct *p)
> > LSM_HOOK(int, 0, task_getsid, struct task_struct *p)
> > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> > index 91c8146649f5..84a0d7e02176 100644
> > --- a/include/linux/lsm_hooks.h
> > +++ b/include/linux/lsm_hooks.h
> > @@ -702,6 +702,13 @@
> > * @old is the set of credentials that are being replaced.
> > * @flags contains one of the LSM_SETID_* values.
> > * Return 0 on success.
> > + * @task_fix_setgroups:
> > + * Update the module's state after setting the supplementary group
> > + * identity attributes of the current process.
> > + * @new is the set of credentials that will be installed. Modifications
> > + * should be made to this rather than to @current->cred.
> > + * @old is the set of credentials that are being replaced.
> > + * Return 0 on success.
> > * @task_setpgid:
> > * Check permission before setting the process group identifier of the
> > * process @p to @pgid.
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index 7fc4e9f49f54..1dfd32c49fa3 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -415,6 +415,7 @@ int security_task_fix_setuid(struct cred *new, const struct cred *old,
> > int flags);
> > int security_task_fix_setgid(struct cred *new, const struct cred *old,
> > int flags);
> > +int security_task_fix_setgroups(struct cred *new, const struct cred *old);
> > int security_task_setpgid(struct task_struct *p, pid_t pgid);
> > int security_task_getpgid(struct task_struct *p);
> > int security_task_getsid(struct task_struct *p);
> > @@ -1098,6 +1099,12 @@ static inline int security_task_fix_setgid(struct cred *new,
> > return 0;
> > }
> > +static inline int security_task_fix_setgroups(struct cred *new,
> > + const struct cred *old)
> > +{
> > + return 0;
> > +}
> > +
> > static inline int security_task_setpgid(struct task_struct *p, pid_t pgid)
> > {
> > return 0;
> > diff --git a/kernel/groups.c b/kernel/groups.c
> > index 787b381c7c00..9aaed2a31073 100644
> > --- a/kernel/groups.c
> > +++ b/kernel/groups.c
> > @@ -134,13 +134,26 @@ EXPORT_SYMBOL(set_groups);
> > int set_current_groups(struct group_info *group_info)
> > {
> > struct cred *new;
> > + const struct cred *old;
> > + int retval;
> > new = prepare_creds();
> > if (!new)
> > return -ENOMEM;
> > + old = current_cred();
> > +
> > set_groups(new, group_info);
> > +
> > + retval = security_task_fix_setgroups(new, old);
> > + if (retval < 0)
> > + goto error;
> > +
> > return commit_creds(new);
> > +
> > +error:
> > + abort_creds(new);
> > + return retval;
> > }
> > EXPORT_SYMBOL(set_current_groups);
> > diff --git a/security/security.c b/security/security.c
> > index 188b8f782220..15c686145ad6 100644
> > --- a/security/security.c
> > +++ b/security/security.c
> > @@ -1803,6 +1803,11 @@ int security_task_fix_setgid(struct cred *new, const struct cred *old,
> > return call_int_hook(task_fix_setgid, 0, new, old, flags);
> > }
> > +int security_task_fix_setgroups(struct cred *new, const struct cred *old)
> > +{
> > + return call_int_hook(task_fix_setgroups, 0, new, old);
> > +}
> > +
> > int security_task_setpgid(struct task_struct *p, pid_t pgid)
> > {
> > return call_int_hook(task_setpgid, 0, p, pgid);