[PATCH 1/2] security: Add LSM hook to setgroups() syscall

Micah Morton
2022-06-13T21:01:24Z

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.

Signed-off-by: Micah Morton <mortonm@chromium.org>
---

Developed on 5.18

include/linux/lsm_hook_defs.h | 1 +
include/linux/lsm_hooks.h | 7 +++++++
include/linux/security.h | 7 +++++++
kernel/groups.c | 12 ++++++++++++
security/security.c | 5 +++++
5 files changed, 32 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index db924fe379c9..c01063ec4be7 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 419b5febc3ca..b5143d9a1127 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -701,6 +701,13 @@
* @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 25b3ef71f495..d111ff830742 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -413,6 +413,7 @@ 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);
@@ -1096,6 +1097,12 @@ 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..c085f54d8dbb 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -134,13 +134,25 @@ EXPORT_SYMBOL(set_groups);
int set_current_groups(struct group_info *group_info)
{
struct cred *new;
+ struct cred *old;

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 b7cf5cbfdc67..eaed8d16d90a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1809,6 +1809,11 @@ 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