The set*uid system calls all call an LSM fixup hook called
security_task_fix_setuid, which allows for altering the behavior of those
calls by a security module. Comments explaining the LSM_SETID_* constants
in /include/linux/security.h imply that the constants are to be used for
both the set*uid and set*gid syscalls, but the set*gid syscalls do not
have the relevant hooks, meaning a security module can only alter syscalls
that change user identity attributes but not ones that change group
identity attributes. This patch adds the necessary LSM hook, called
security_task_fix_setgid, and calls the hook from the appropriate places
in the set*gid syscalls.Tested by putting a print statement in the hook and
seeing it triggered from the various set*gid syscalls.
---
NOTE: the security_task_fix_setgid line in sys_setfsgid is over 80
characters, but I figured I'd just follow how it was done in sys_setfsuid
rather than trying to wrap the line, since the functions are nearly
identical.
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 8f1131c8dd54..a2166c812a97 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -599,6 +599,15 @@
 * @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:
+ *Â Â ÂUpdate the module's state after setting one or more of the group
+ *  Âidentity attributes of the current process. The @flags parameter
+ *Â Â Âindicates which of the set*gid system calls invoked this hook.
+ *  Â@new is the set of credentials that will be installed. Modifications
+ *Â Â Âshould be made to this rather than to @current->cred.
+ *Â Â Â@old is the set of credentials that are being replaced
+ *Â Â Â@flags contains one of the LSM_SETID_* values.
+ *Â Â ÂReturn 0 on success.
 * @task_setpgid:
 * Check permission before setting the process group identifier of the
 * process @p to @pgid.
@@ -1587,6 +1596,8 @@ union security_list_options {
   Âenum 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);
@@ -1876,6 +1887,7 @@ 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 63030c85ee19..a82d97cf13ab 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -325,6 +325,8 @@ int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
  Âenum kernel_read_file_id id);
Âint security_task_fix_setuid(struct cred *new, const struct cred *old,
   Âint flags);
+int security_task_fix_setgid(struct cred *new, const struct cred *old,
+ Â Â Âint flags);
Âint security_task_setpgid(struct task_struct *p, pid_t pgid);
Âint security_task_getpgid(struct task_struct *p);
Âint security_task_getsid(struct task_struct *p);
@@ -929,6 +931,13 @@ static inline int security_task_fix_setuid(struct cred *new,
 return cap_task_fix_setuid(new, old, flags);
Â}
Â
+static inline int security_task_fix_setgid(struct cred *new,
+ Â Âconst struct cred *old,
+ Â Âint flags)
+{
+ return 0;
+}
+
Âstatic inline int security_task_setpgid(struct task_struct *p, pid_t pgid)
Â{
 return 0;
diff --git a/kernel/sys.c b/kernel/sys.c
index 38509dc1f77b..f6ef922c6815 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -392,6 +392,10 @@ long __sys_setregid(gid_t rgid, gid_t egid)
 new->sgid = new->egid;
 new->fsgid = new->egid;
Â
+ retval = security_task_fix_setgid(new, old, LSM_SETID_RE);
+ if (retval < 0)
+ goto error;
+
 return commit_creds(new);
Â
Âerror:
@@ -434,6 +438,10 @@ long __sys_setgid(gid_t gid)
 else
 goto error;
Â
+ retval = security_task_fix_setgid(new, old, LSM_SETID_ID);
+ if (retval < 0)
+ goto error;
+
 return commit_creds(new);
Â
Âerror:
@@ -755,6 +763,10 @@ long __sys_setresgid(gid_t rgid, gid_t egid, gid_t sgid)
 new->sgid = ksgid;
 new->fsgid = new->egid;
Â
+ retval = security_task_fix_setgid(new, old, LSM_SETID_RES);
+ if (retval < 0)
+ goto error;
+
 return commit_creds(new);
Â
Âerror:
@@ -861,7 +873,8 @@ long __sys_setfsgid(gid_t gid)
   ns_capable(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;
 }
 }
Â
diff --git a/security/security.c b/security/security.c
index 68f46d849abe..587786fc0aaa 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1062,6 +1062,12 @@ int security_task_fix_setuid(struct cred *new, const struct cred *old,
 return call_int_hook(task_fix_setuid, 0, new, old, flags);
Â}
Â
+int security_task_fix_setgid(struct cred *new, const struct cred *old,
+ Â Â Âint flags)
+{
+ return call_int_hook(task_fix_setgid, 0, new, old, flags);
+}
+
Âint security_task_setpgid(struct task_struct *p, pid_t pgid)
Â{
 return call_int_hook(task_setpgid, 0, p, pgid);