[PATCH v4 1/2] LSM: SafeSetID: gate setgid transitions

From: mortonm@chromium.org
Date: 2019-02-28 23:55:39
Subsystem: capabilities, documentation, safesetid security module, security subsystem, the rest · Maintainers: Serge Hallyn, Jonathan Corbet, Micah Morton, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds

From: Micah Morton <mortonm@chromium.org>

This patch generalizes the 'task_fix_setuid' LSM hook to enable hooking
setgid transitions as well as setuid transitions. The hook is renamed to
'task_fix_setid'. The patch introduces calls to this 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 patch
also makes sure the setgid functions in kernel/sys.c call
security_capable_setid rather than the ordinary security_capable
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>
---
Changes since the last patch: Add break statements for the
setgid-related case statements in cap_task_fix_setid in
security/commoncap.c. We don't want those cases to fall through to the
default statement and return -EINVAL. Are the setreuid and setuid cases
for this function always returning -EINVAL or am I missing something
really obvious?.. Seems strange if that is the case.

 Documentation/admin-guide/LSM/SafeSetID.rst |  2 +-
 include/linux/lsm_hooks.h                   |  8 ++---
 include/linux/security.h                    | 36 ++++++++++++++-------
 kernel/sys.c                                | 35 ++++++++++++++------
 security/commoncap.c                        | 25 +++++++++-----
 security/safesetid/lsm.c                    | 12 +++----
 security/security.c                         |  4 +--
 7 files changed, 79 insertions(+), 43 deletions(-)

diff --git a/Documentation/admin-guide/LSM/SafeSetID.rst b/Documentation/admin-guide/LSM/SafeSetID.rst
index 212434ef65ad..670a6544fd39 100644
--- a/Documentation/admin-guide/LSM/SafeSetID.rst
+++ b/Documentation/admin-guide/LSM/SafeSetID.rst

@@ -88,7 +88,7 @@ other system interactions, including use of pid namespaces and device creation.
 Use an existing LSM
 -------------------
 None of the other in-tree LSMs have the capability to gate setid transitions, or
-even employ the security_task_fix_setuid hook at all. SELinux says of that hook:
+even employ the security_task_fix_setid hook at all. SELinux says of that hook:
 "Since setuid only affects the current process, and since the SELinux controls
 are not based on the Linux identity attributes, SELinux does not need to control
 this operation."

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 22fc786d723a..47fd04410fde 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h

@@ -594,14 +594,14 @@
  *	@size length of the file contents.
  *	@id kernel read file identifier
  *	Return 0 if permission is granted.
- * @task_fix_setuid:
+ * @task_fix_setid:
  *	Update the module's state after setting one or more of the user
  *	identity attributes of the current process.  The @flags parameter
  *	indicates which of the set*uid system calls invoked this hook.  If
  *	@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 replaces
- *	@flags contains one of the LSM_SETID_* values.
+ *	@flags contains one of the LSM_SET*ID_* values.
  *	Return 0 on success.
  * @task_setpgid:
  *	Check permission before setting the process group identifier of the

@@ -1594,7 +1594,7 @@ union security_list_options {
 	int (*kernel_read_file)(struct file *file, enum kernel_read_file_id id);
 	int (*kernel_post_read_file)(struct file *file, char *buf, loff_t size,
 				     enum kernel_read_file_id id);
-	int (*task_fix_setuid)(struct cred *new, const struct cred *old,
+	int (*task_fix_setid)(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);

@@ -1886,7 +1886,7 @@ struct security_hook_heads {
 	struct hlist_head kernel_read_file;
 	struct hlist_head kernel_post_read_file;
 	struct hlist_head kernel_module_request;
-	struct hlist_head task_fix_setuid;
+	struct hlist_head task_fix_setid;
 	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..76df3e22fed1 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h

@@ -95,7 +95,7 @@ extern int cap_inode_getsecurity(struct inode *inode, const char *name,
 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_setid(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);

@@ -128,17 +128,29 @@ extern unsigned long dac_mmap_min_addr;
 /*
  * Values used in the task_security_ops calls
  */
-/* setuid or setgid, id0 == uid or gid */
-#define LSM_SETID_ID	1
+/* setuid, id0 == uid */
+#define LSM_SETUID_ID	1
 
-/* setreuid or setregid, id0 == real, id1 == eff */
-#define LSM_SETID_RE	2
+/* setreuid, id0 == real, id1 == eff */
+#define LSM_SETUID_RE	2
 
-/* setresuid or setresgid, id0 == real, id1 == eff, uid2 == saved */
-#define LSM_SETID_RES	4
+/* setresuid, id0 == real, id1 == eff, uid2 == saved */
+#define LSM_SETUID_RES	4
 
-/* setfsuid or setfsgid, id0 == fsuid or fsgid */
-#define LSM_SETID_FS	8
+/* setfsuid, id0 == fsgid */
+#define LSM_SETUID_FS	8
+
+/* setgid, id0 == gid */
+#define LSM_SETGID_ID	16
+
+/* setregid, id0 == real, id1 == eff */
+#define LSM_SETGID_RE	32
+
+/* setresgid, id0 == real, id1 == eff, uid2 == saved */
+#define LSM_SETGID_RES	64
+
+/* setfsgid, id0 == fsgid */
+#define LSM_SETGID_FS	128
 
 /* Flags for security_task_prlimit(). */
 #define LSM_PRLIMIT_READ  1

@@ -324,7 +336,7 @@ int security_kernel_load_data(enum kernel_load_data_id id);
 int security_kernel_read_file(struct file *file, enum kernel_read_file_id id);
 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 security_task_fix_setid(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);

@@ -923,11 +935,11 @@ static inline int security_kernel_post_read_file(struct file *file,
 	return 0;
 }
 
-static inline int security_task_fix_setuid(struct cred *new,
+static inline int security_task_fix_setid(struct cred *new,
 					   const struct cred *old,
 					   int flags)
 {
-	return cap_task_fix_setuid(new, old, flags);
+	return cap_task_fix_setid(new, old, flags);
 }
 
 static inline int security_task_setpgid(struct task_struct *p, pid_t pgid)

diff --git a/kernel/sys.c b/kernel/sys.c
index c5f875048aef..615b44939238 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_setid(new, old, LSM_SETGID_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_setid(new, old, LSM_SETGID_ID);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:

@@ -539,7 +547,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
 		new->suid = new->euid;
 	new->fsuid = new->euid;
 
-	retval = security_task_fix_setuid(new, old, LSM_SETID_RE);
+	retval = security_task_fix_setid(new, old, LSM_SETUID_RE);
 	if (retval < 0)
 		goto error;

@@ -597,7 +605,7 @@ long __sys_setuid(uid_t uid)
 
 	new->fsuid = new->euid = kuid;
 
-	retval = security_task_fix_setuid(new, old, LSM_SETID_ID);
+	retval = security_task_fix_setid(new, old, LSM_SETUID_ID);
 	if (retval < 0)
 		goto error;

@@ -672,7 +680,7 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
 		new->suid = ksuid;
 	new->fsuid = new->euid;
 
-	retval = security_task_fix_setuid(new, old, LSM_SETID_RES);
+	retval = security_task_fix_setid(new, old, LSM_SETUID_RES);
 	if (retval < 0)
 		goto 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_setid(new, old, LSM_SETGID_RES);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:

@@ -817,7 +829,7 @@ long __sys_setfsuid(uid_t uid)
 	    ns_capable_setid(old->user_ns, CAP_SETUID)) {
 		if (!uid_eq(kuid, old->fsuid)) {
 			new->fsuid = kuid;
-			if (security_task_fix_setuid(new, old, LSM_SETID_FS) == 0)
+			if (security_task_fix_setid(new, old, LSM_SETUID_FS) == 0)
 				goto change_okay;
 		}
 	}

@@ -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_setid(new,
+						old,
+						LSM_SETGID_FS) == 0)
+				goto change_okay;
 		}
 	}

diff --git a/security/commoncap.c b/security/commoncap.c
index f1d117c3d8ae..6f514d91d010 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c

@@ -1026,27 +1026,27 @@ static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
 }
 
 /**
- * cap_task_fix_setuid - Fix up the results of setuid() call
+ * cap_task_fix_setid - Fix up the results of setid() call
  * @new: The proposed credentials
  * @old: The current task's current credentials
  * @flags: Indications of what has changed
  *
- * Fix up the results of setuid() call before the credential changes are
+ * Fix up the results of setid() call before the credential changes are
  * actually applied, returning 0 to grant the changes, -ve to deny them.
  */
-int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
+int cap_task_fix_setid(struct cred *new, const struct cred *old, int flags)
 {
 	switch (flags) {
-	case LSM_SETID_RE:
-	case LSM_SETID_ID:
-	case LSM_SETID_RES:
+	case LSM_SETUID_RE:
+	case LSM_SETUID_ID:
+	case LSM_SETUID_RES:
 		/* juggle the capabilities to follow [RES]UID changes unless
 		 * otherwise suppressed */
 		if (!issecure(SECURE_NO_SETUID_FIXUP))
 			cap_emulate_setxuid(new, old);
 		break;
 
-	case LSM_SETID_FS:
+	case LSM_SETUID_FS:
 		/* juggle the capabilties to follow FSUID changes, unless
 		 * otherwise suppressed
 		 *

@@ -1066,6 +1066,15 @@ int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
 		}
 		break;
 
+	case LSM_SETGID_RE:
+                break;
+	case LSM_SETGID_ID:
+                break;
+	case LSM_SETGID_RES:
+                break;
+	case LSM_SETGID_FS:
+                break;
+
 	default:
 		return -EINVAL;
 	}

@@ -1355,7 +1364,7 @@ struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),
 	LSM_HOOK_INIT(mmap_addr, cap_mmap_addr),
 	LSM_HOOK_INIT(mmap_file, cap_mmap_file),
-	LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid),
+	LSM_HOOK_INIT(task_fix_setid, cap_task_fix_setid),
 	LSM_HOOK_INIT(task_prctl, cap_task_prctl),
 	LSM_HOOK_INIT(task_setscheduler, cap_task_setscheduler),
 	LSM_HOOK_INIT(task_setioprio, cap_task_setioprio),

diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c
index cecd38e2ac80..5deffa92f25f 100644
--- a/security/safesetid/lsm.c
+++ b/security/safesetid/lsm.c

@@ -120,7 +120,7 @@ static int check_uid_transition(kuid_t parent, kuid_t child)
  * set*uid to user under new cred struct, or the UID transition is allowed (by
  * Linux set*uid rules) even without CAP_SETUID.
  */
-static int safesetid_task_fix_setuid(struct cred *new,
+static int safesetid_task_fix_setid(struct cred *new,
 				     const struct cred *old,
 				     int flags)
 {

@@ -130,7 +130,7 @@ static int safesetid_task_fix_setuid(struct cred *new,
 		return 0;
 
 	switch (flags) {
-	case LSM_SETID_RE:
+	case LSM_SETUID_RE:
 		/*
 		 * Users for which setuid restrictions exist can only set the
 		 * real UID to the real UID or the effective UID, unless an

@@ -152,7 +152,7 @@ static int safesetid_task_fix_setuid(struct cred *new,
 			return check_uid_transition(old->euid, new->euid);
 		}
 		break;
-	case LSM_SETID_ID:
+	case LSM_SETUID_ID:
 		/*
 		 * Users for which setuid restrictions exist cannot change the
 		 * real UID or saved set-UID unless an explicit whitelist

@@ -163,7 +163,7 @@ static int safesetid_task_fix_setuid(struct cred *new,
 		if (!uid_eq(old->suid, new->suid))
 			return check_uid_transition(old->suid, new->suid);
 		break;
-	case LSM_SETID_RES:
+	case LSM_SETUID_RES:
 		/*
 		 * Users for which setuid restrictions exist cannot change the
 		 * real UID, effective UID, or saved set-UID to anything but

@@ -187,7 +187,7 @@ static int safesetid_task_fix_setuid(struct cred *new,
 			return check_uid_transition(old->suid, new->suid);
 		}
 		break;
-	case LSM_SETID_FS:
+	case LSM_SETUID_FS:
 		/*
 		 * Users for which setuid restrictions exist cannot change the
 		 * filesystem UID to anything but one of: the current real UID,

@@ -256,7 +256,7 @@ void flush_safesetid_whitelist_entries(void)
 }
 
 static struct security_hook_list safesetid_security_hooks[] = {
-	LSM_HOOK_INIT(task_fix_setuid, safesetid_task_fix_setuid),
+	LSM_HOOK_INIT(task_fix_setid, safesetid_task_fix_setid),
 	LSM_HOOK_INIT(capable, safesetid_security_capable)
 };

diff --git a/security/security.c b/security/security.c
index ed9b8cbf21cf..450784fd1d2b 100644
--- a/security/security.c
+++ b/security/security.c

@@ -1568,10 +1568,10 @@ int security_kernel_load_data(enum kernel_load_data_id id)
 }
 EXPORT_SYMBOL_GPL(security_kernel_load_data);
 
-int security_task_fix_setuid(struct cred *new, const struct cred *old,
+int security_task_fix_setid(struct cred *new, const struct cred *old,
 			     int flags)
 {
-	return call_int_hook(task_fix_setuid, 0, new, old, flags);
+	return call_int_hook(task_fix_setid, 0, new, old, flags);
 }
 
 int security_task_setpgid(struct task_struct *p, pid_t pgid)

-- 
2.21.0.352.gf09ad66450-goog

`h`	back out one level
`j`	next message in thread
`k`	previous message in thread
`l`	drill in
`Esc`	close help / fold thread tree
`?`	toggle this help