security: Add LSM hooks to set*gid syscalls
diff mbox series

Message ID 20200605193805.36531-1-mortonm@chromium.org
State New
Headers show
Series
  • security: Add LSM hooks to set*gid syscalls
Related show

Commit Message

Micah Morton June 5, 2020, 7:38 p.m. UTC
The SafeSetID LSM uses the security_task_fix_setuid hook to filter
set*uid() syscalls according to its configured security policy. In
preparation for adding analagous support in the LSM for set*gid()
syscalls, we add the requisite hook here. Tested by putting print
statements in the security_task_fix_setgid hook and seeing them get hit
during kernel boot.

From: Thomas Cedeno <thomascedeno@google.com>
Signed-off-by: Thomas Cedeno <thomascedeno@google.com>
Reviewed-by: Micah Morton <mortonm@chromium.org>
---
NOTE: I (Micah) will send this patch as a pull request to Linus through
my SafeSetID tree if there are no objections.
 include/linux/lsm_hook_defs.h |  2 ++
 include/linux/lsm_hooks.h     |  9 +++++++++
 include/linux/security.h      |  9 +++++++++
 kernel/sys.c                  | 15 ++++++++++++++-
 security/security.c           |  6 ++++++
 5 files changed, 40 insertions(+), 1 deletion(-)

Comments

Kees Cook June 5, 2020, 9:25 p.m. UTC | #1
On Fri, Jun 05, 2020 at 12:38:05PM -0700, Micah Morton wrote:
> The SafeSetID LSM uses the security_task_fix_setuid hook to filter
> set*uid() syscalls according to its configured security policy. In
> preparation for adding analagous support in the LSM for set*gid()
> syscalls, we add the requisite hook here. Tested by putting print
> statements in the security_task_fix_setgid hook and seeing them get hit
> during kernel boot.
> 
> From: Thomas Cedeno <thomascedeno@google.com>

^^^ this line should be before the commit log body (many tools won't
find it here).

> Signed-off-by: Thomas Cedeno <thomascedeno@google.com>
> Reviewed-by: Micah Morton <mortonm@chromium.org>
> ---
> NOTE: I (Micah) will send this patch as a pull request to Linus through
> my SafeSetID tree if there are no objections.
>  include/linux/lsm_hook_defs.h |  2 ++
>  include/linux/lsm_hooks.h     |  9 +++++++++
>  include/linux/security.h      |  9 +++++++++
>  kernel/sys.c                  | 15 ++++++++++++++-
>  security/security.c           |  6 ++++++
>  5 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index fb3ce6cec997..d5401c09f2d3 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -191,6 +191,8 @@ LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,
>  	 loff_t size, enum kernel_read_file_id id)
>  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_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 3e62dab77699..8012b610fe53 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -659,6 +659,15 @@
>   *	@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.

The indenting here appears to be using spaces instead of a tab.

Everything else looks okay. (There are a surprising number of gid
changing places...)
Micah Morton June 5, 2020, 10:51 p.m. UTC | #2
On Fri, Jun 5, 2020 at 2:25 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Jun 05, 2020 at 12:38:05PM -0700, Micah Morton wrote:
> > The SafeSetID LSM uses the security_task_fix_setuid hook to filter
> > set*uid() syscalls according to its configured security policy. In
> > preparation for adding analagous support in the LSM for set*gid()
> > syscalls, we add the requisite hook here. Tested by putting print
> > statements in the security_task_fix_setgid hook and seeing them get hit
> > during kernel boot.
> >
> > From: Thomas Cedeno <thomascedeno@google.com>
>
> ^^^ this line should be before the commit log body (many tools won't
> find it here).
>
> > Signed-off-by: Thomas Cedeno <thomascedeno@google.com>
> > Reviewed-by: Micah Morton <mortonm@chromium.org>
> > ---
> > NOTE: I (Micah) will send this patch as a pull request to Linus through
> > my SafeSetID tree if there are no objections.
> >  include/linux/lsm_hook_defs.h |  2 ++
> >  include/linux/lsm_hooks.h     |  9 +++++++++
> >  include/linux/security.h      |  9 +++++++++
> >  kernel/sys.c                  | 15 ++++++++++++++-
> >  security/security.c           |  6 ++++++
> >  5 files changed, 40 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> > index fb3ce6cec997..d5401c09f2d3 100644
> > --- a/include/linux/lsm_hook_defs.h
> > +++ b/include/linux/lsm_hook_defs.h
> > @@ -191,6 +191,8 @@ LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,
> >        loff_t size, enum kernel_read_file_id id)
> >  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_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 3e62dab77699..8012b610fe53 100644
> > --- a/include/linux/lsm_hooks.h
> > +++ b/include/linux/lsm_hooks.h
> > @@ -659,6 +659,15 @@
> >   *   @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.
>
> The indenting here appears to be using spaces instead of a tab.
>
> Everything else looks okay. (There are a surprising number of gid
> changing places...)

Ah thanks! I'll fix those 2 things before doing the pull request.
Probably not worth doing a patch resend.

Will still give it some time to see if anyone else wants to comment.

>
> --
> Kees Cook

Patch
diff mbox series

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index fb3ce6cec997..d5401c09f2d3 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -191,6 +191,8 @@  LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,
 	 loff_t size, enum kernel_read_file_id id)
 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_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 3e62dab77699..8012b610fe53 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -659,6 +659,15 @@ 
  *	@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.
diff --git a/include/linux/security.h b/include/linux/security.h
index b3f2cb21b4f2..2b08a2e49ba6 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -390,6 +390,8 @@  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);
@@ -1034,6 +1036,13 @@  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 0;
+}
+
 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 891667a49bb7..e65ec850bfae 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -393,6 +393,10 @@  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:
@@ -435,6 +439,10 @@  long __sys_setgid(gid_t gid)
 	else
 		goto error;
 
+	retval = security_task_fix_setgid(new, old, LSM_SETID_ID);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:
@@ -756,6 +764,10 @@  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:
@@ -862,7 +874,8 @@  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;
 		}
 	}
 
diff --git a/security/security.c b/security/security.c
index 11c1a7da4fd1..639324c68dd0 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1690,6 +1690,12 @@  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);