On Tue, Feb 19, 2019 at 09:00:13AM -0800, Micah Morton wrote:

On Sat, Feb 16, 2019 at 8:43 AM Serge E. Hallyn [off-list ref] wrote:

quoted

On Fri, Feb 15, 2019 at 02:22:17PM -0800, mortonm@chromium.org wrote:

quoted

From: Micah Morton <mortonm@chromium.org>

This patch adds a 'task_fix_setgid' LSM hook, which is analogous to the
existing 'task_fix_setuid' LSM hook, and calls this new hook from the
setgid functions in kernel/sys.c. This will allow the SafeSetID LSM to
govern setgid transitions in addition to setuid transitions. This change
also makes sure the setgid functions in kernel/sys.c call
security_capable_setid rather than the ordinary security_capable

Sorry, where security_capable_setid this defined?  I assume it was in a recent
patchset, but google and grep are failing me.

It was defined in commit 40852275a94afb3e836be9248399e036982d1a79 on
the origin/next-general branch of
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git.

Thanks.

quoted

quoted

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>

Acked-by: Serge Hallyn <serge@hallyn.com>

quoted

quoted

---
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