function, so that the security_capable hook in the SafeSetID LSM knows
it is being invoked from a setid function.

Signed-off-by: Micah Morton <mortonm@chromium.org>
---
Tested with slight mod to test in tools/testing/selftests/safesetid for
testing setgid as well as setuid.

 include/linux/lsm_hooks.h | 12 ++++++++++++
 include/linux/security.h  | 10 ++++++++++
 kernel/sys.c              | 27 +++++++++++++++++++++------
 security/security.c       |  6 ++++++
 4 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 22fc786d723a..f252ed3e95ef 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h

@@ -603,6 +603,15 @@
  *	@old is the set of credentials that are being replaces
  *	@flags contains one of the LSM_SETID_* values.
  *	Return 0 on success.
+ * @task_fix_setgid:
+ *      Update the module's state after setting one or more of the group
+ *      identity attributes of the current process.  The @flags parameter
+ *      indicates which of the set*gid system calls invoked this hook.
+ *      @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
+ *      @flags contains one of the LSM_SETID_* values.
+ *      Return 0 on success.
  * @task_setpgid:
  *	Check permission before setting the process group identifier of the
  *	process @p to @pgid.

@@ -1596,6 +1605,8 @@ union security_list_options {
 				     enum kernel_read_file_id id);
 	int (*task_fix_setuid)(struct cred *new, const struct cred *old,
 				int flags);
+	int (*task_fix_setgid)(struct cred *new, const struct cred *old,
+				int flags);
 	int (*task_setpgid)(struct task_struct *p, pid_t pgid);
 	int (*task_getpgid)(struct task_struct *p);
 	int (*task_getsid)(struct task_struct *p);

@@ -1887,6 +1898,7 @@ struct security_hook_heads {
 	struct hlist_head kernel_post_read_file;
 	struct hlist_head kernel_module_request;
 	struct hlist_head task_fix_setuid;
+	struct hlist_head task_fix_setgid;
 	struct hlist_head task_setpgid;
 	struct hlist_head task_getpgid;
 	struct hlist_head task_getsid;

diff --git a/include/linux/security.h b/include/linux/security.h
index 13537a49ae97..f3d095e8dfc1 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h

@@ -96,6 +96,7 @@ extern int cap_mmap_addr(unsigned long addr);
 extern int cap_mmap_file(struct file *file, unsigned long reqprot,
 			 unsigned long prot, unsigned long flags);
 extern int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags);
+extern int cap_task_fix_setgid(struct cred *new, const struct cred *old, int flags);
 extern int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 			  unsigned long arg4, unsigned long arg5);
 extern int cap_task_setscheduler(struct task_struct *p);

@@ -326,6 +327,8 @@ int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
 				   enum kernel_read_file_id id);
 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_setpgid(struct task_struct *p, pid_t pgid);
 int security_task_getpgid(struct task_struct *p);
 int security_task_getsid(struct task_struct *p);

@@ -930,6 +933,13 @@ static inline int security_task_fix_setuid(struct cred *new,
 	return cap_task_fix_setuid(new, old, flags);
 }
 
+static inline int security_task_fix_setgid(struct cred *new,
+					   const struct cred *old,
+					   int flags)
+{
+	return cap_task_fix_setgid(new, old, flags);
+}
+
 static inline int security_task_setpgid(struct task_struct *p, pid_t pgid)
 {
 	return 0;

diff --git a/kernel/sys.c b/kernel/sys.c
index c5f875048aef..76f1c46ac66f 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c

@@ -372,7 +372,7 @@ long __sys_setregid(gid_t rgid, gid_t egid)
 	if (rgid != (gid_t) -1) {
 		if (gid_eq(old->gid, krgid) ||
 		    gid_eq(old->egid, krgid) ||
-		    ns_capable(old->user_ns, CAP_SETGID))
+		    ns_capable_setid(old->user_ns, CAP_SETGID))
 			new->gid = krgid;
 		else
 			goto error;

@@ -381,7 +381,7 @@ long __sys_setregid(gid_t rgid, gid_t egid)
 		if (gid_eq(old->gid, kegid) ||
 		    gid_eq(old->egid, kegid) ||
 		    gid_eq(old->sgid, kegid) ||
-		    ns_capable(old->user_ns, CAP_SETGID))
+		    ns_capable_setid(old->user_ns, CAP_SETGID))
 			new->egid = kegid;
 		else
 			goto error;

@@ -392,6 +392,10 @@ long __sys_setregid(gid_t rgid, gid_t egid)
 		new->sgid = new->egid;
 	new->fsgid = new->egid;
 
+	retval = security_task_fix_setgid(new, old, LSM_SETID_RE);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:

@@ -427,13 +431,17 @@ long __sys_setgid(gid_t gid)
 	old = current_cred();
 
 	retval = -EPERM;
-	if (ns_capable(old->user_ns, CAP_SETGID))
+	if (ns_capable_setid(old->user_ns, CAP_SETGID))
 		new->gid = new->egid = new->sgid = new->fsgid = kgid;
 	else if (gid_eq(kgid, old->gid) || gid_eq(kgid, old->sgid))
 		new->egid = new->fsgid = kgid;
 	else
 		goto error;
 
+	retval = security_task_fix_setgid(new, old, LSM_SETID_ID);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:

@@ -735,7 +743,7 @@ long __sys_setresgid(gid_t rgid, gid_t egid, gid_t sgid)
 	old = current_cred();
 
 	retval = -EPERM;
-	if (!ns_capable(old->user_ns, CAP_SETGID)) {
+	if (!ns_capable_setid(old->user_ns, CAP_SETGID)) {
 		if (rgid != (gid_t) -1        && !gid_eq(krgid, old->gid) &&
 		    !gid_eq(krgid, old->egid) && !gid_eq(krgid, old->sgid))
 			goto error;

@@ -755,6 +763,10 @@ long __sys_setresgid(gid_t rgid, gid_t egid, gid_t sgid)
 		new->sgid = ksgid;
 	new->fsgid = new->egid;
 
+	retval = security_task_fix_setgid(new, old, LSM_SETID_RES);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:

@@ -858,10 +870,13 @@ long __sys_setfsgid(gid_t gid)
 
 	if (gid_eq(kgid, old->gid)  || gid_eq(kgid, old->egid)  ||
 	    gid_eq(kgid, old->sgid) || gid_eq(kgid, old->fsgid) ||
-	    ns_capable(old->user_ns, CAP_SETGID)) {
+	    ns_capable_setid(old->user_ns, CAP_SETGID)) {
 		if (!gid_eq(kgid, old->fsgid)) {
 			new->fsgid = kgid;
-			goto change_okay;
+			if (security_task_fix_setgid(new,
+						old,
+						LSM_SETID_FS) == 0)
+				goto change_okay;
 		}
 	}
 

diff --git a/security/security.c b/security/security.c
index b6bff646d373..4264a1e77ce8 100644
--- a/security/security.c
+++ b/security/security.c

@@ -1570,6 +1570,12 @@ int security_task_fix_setuid(struct cred *new, const struct cred *old,
 	return call_int_hook(task_fix_setuid, 0, new, old, flags);
 }
 
+int security_task_fix_setgid(struct cred *new, const struct cred *old,
+			     int flags)
+{
+	return call_int_hook(task_fix_setgid, 0, new, old, flags);
+}
+
 int security_task_setpgid(struct task_struct *p, pid_t pgid)
 {
 	return call_int_hook(task_setpgid, 0, p, pgid);

-- 
2.21.0.rc0.258.g878e2cd30e-goog