exec: Factor security_bprm_creds_for_exec out of security_bprm_set_creds

Today security_bprm_set_creds has several implementations:
apparmor_bprm_set_creds, cap_bprm_set_creds, selinux_bprm_set_creds,
smack_bprm_set_creds, and tomoyo_bprm_set_creds.

Except for cap_bprm_set_creds they all test bprm->called_set_creds and
return immediately if it is true.  The function cap_bprm_set_creds
ignores bprm->calld_sed_creds entirely.

Create a new LSM hook security_bprm_creds_for_exec that is called just
before prepare_binprm in __do_execve_file, resulting in a LSM hook
that is called exactly once for the entire of exec.  Modify the bits
of security_bprm_set_creds that only want to be called once per exec
into security_bprm_creds_for_exec, leaving only cap_bprm_set_creds
behind.

Remove bprm->called_set_creds all of it's former users have been moved
to security_bprm_creds_for_exec.

Add or upate comments a appropriate to bring them up to date and
to reflect this change.

Link: https://lkml.kernel.org/r/87v9kszrzh.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com> # For the LSM and Smack bits
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

7 files changed, 18 insertions, 27 deletions

diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index 6ceb74e0f789..0b870a647488 100644
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -854,14 +854,14 @@ static struct aa_label *handle_onexec(struct aa_label *label,
 }
 
 /**
- * apparmor_bprm_set_creds - set the new creds on the bprm struct
+ * apparmor_bprm_creds_for_exec - Update the new creds on the bprm struct
  * @bprm: binprm for the exec  (NOT NULL)
  *
  * Returns: %0 or error on failure
  *
  * TODO: once the other paths are done see if we can't refactor into a fn
  */
-int apparmor_bprm_set_creds(struct linux_binprm *bprm)
+int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
 {
 	struct aa_task_ctx *ctx;
 	struct aa_label *label, *new = NULL;
@@ -875,9 +875,6 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 		file_inode(bprm->file)->i_mode
 	};
 
-	if (bprm->called_set_creds)
-		return 0;
-
 	ctx = task_ctx(current);
 	AA_BUG(!cred_label(bprm->cred));
 	AA_BUG(!ctx);
diff --git a/security/apparmor/include/domain.h b/security/apparmor/include/domain.h
index 21b875fe2d37..d14928fe1c6f 100644
--- a/security/apparmor/include/domain.h
+++ b/security/apparmor/include/domain.h
@@ -30,7 +30,7 @@ struct aa_domain {
 struct aa_label *x_table_lookup(struct aa_profile *profile, u32 xindex,
 				const char **name);
 
-int apparmor_bprm_set_creds(struct linux_binprm *bprm);
+int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm);
 
 void aa_free_domain_entries(struct aa_domain *domain);
 int aa_change_hat(const char *hats[], int count, u64 token, int flags);
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index b621ad74f54a..3623ab08279d 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1232,7 +1232,7 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(cred_prepare, apparmor_cred_prepare),
 	LSM_HOOK_INIT(cred_transfer, apparmor_cred_transfer),
 
-	LSM_HOOK_INIT(bprm_set_creds, apparmor_bprm_set_creds),
+	LSM_HOOK_INIT(bprm_creds_for_exec, apparmor_bprm_creds_for_exec),
 	LSM_HOOK_INIT(bprm_committing_creds, apparmor_bprm_committing_creds),
 	LSM_HOOK_INIT(bprm_committed_creds, apparmor_bprm_committed_creds),
 
diff --git a/security/security.c b/security/security.c
index 7fed24b9d57e..4ee76a729f73 100644
--- a/security/security.c
+++ b/security/security.c
@@ -823,6 +823,11 @@ int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
 	return __vm_enough_memory(mm, pages, cap_sys_admin);
 }
 
+int security_bprm_creds_for_exec(struct linux_binprm *bprm)
+{
+	return call_int_hook(bprm_creds_for_exec, 0, bprm);
+}
+
 int security_bprm_set_creds(struct linux_binprm *bprm)
 {
 	return call_int_hook(bprm_set_creds, 0, bprm);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 0b4e32161b77..718345dd76bb 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2286,7 +2286,7 @@ static int check_nnp_nosuid(const struct linux_binprm *bprm,
 	return -EACCES;
 }
 
-static int selinux_bprm_set_creds(struct linux_binprm *bprm)
+static int selinux_bprm_creds_for_exec(struct linux_binprm *bprm)
 {
 	const struct task_security_struct *old_tsec;
 	struct task_security_struct *new_tsec;
@@ -2297,8 +2297,6 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm)
 
 	/* SELinux context only depends on initial program or script and not
 	 * the script interpreter */
-	if (bprm->called_set_creds)
-		return 0;
 
 	old_tsec = selinux_cred(current_cred());
 	new_tsec = selinux_cred(bprm->cred);
@@ -6385,7 +6383,7 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 	/* Permission checking based on the specified context is
 	   performed during the actual operation (execve,
 	   open/mkdir/...), when we know the full context of the
-	   operation.  See selinux_bprm_set_creds for the execve
+	   operation.  See selinux_bprm_creds_for_exec for the execve
 	   checks and may_create for the file creation checks. The
 	   operation will then fail if the context is not permitted. */
 	tsec = selinux_cred(new);
@@ -6914,7 +6912,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 
 	LSM_HOOK_INIT(netlink_send, selinux_netlink_send),
 
-	LSM_HOOK_INIT(bprm_set_creds, selinux_bprm_set_creds),
+	LSM_HOOK_INIT(bprm_creds_for_exec, selinux_bprm_creds_for_exec),
 	LSM_HOOK_INIT(bprm_committing_creds, selinux_bprm_committing_creds),
 	LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),
 
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 8c61d175e195..0ac8f4518d07 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -891,12 +891,12 @@ static int smack_sb_statfs(struct dentry *dentry)
  */
 
 /**
- * smack_bprm_set_creds - set creds for exec
+ * smack_bprm_creds_for_exec - Update bprm->cred if needed for exec
  * @bprm: the exec information
  *
  * Returns 0 if it gets a blob, -EPERM if exec forbidden and -ENOMEM otherwise
  */
-static int smack_bprm_set_creds(struct linux_binprm *bprm)
+static int smack_bprm_creds_for_exec(struct linux_binprm *bprm)
 {
 	struct inode *inode = file_inode(bprm->file);
 	struct task_smack *bsp = smack_cred(bprm->cred);
@@ -904,9 +904,6 @@ static int smack_bprm_set_creds(struct linux_binprm *bprm)
 	struct superblock_smack *sbsp;
 	int rc;
 
-	if (bprm->called_set_creds)
-		return 0;
-
 	isp = smack_inode(inode);
 	if (isp->smk_task == NULL || isp->smk_task == bsp->smk_task)
 		return 0;
@@ -4598,7 +4595,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(sb_statfs, smack_sb_statfs),
 	LSM_HOOK_INIT(sb_set_mnt_opts, smack_set_mnt_opts),
 
-	LSM_HOOK_INIT(bprm_set_creds, smack_bprm_set_creds),
+	LSM_HOOK_INIT(bprm_creds_for_exec, smack_bprm_creds_for_exec),
 
 	LSM_HOOK_INIT(inode_alloc_security, smack_inode_alloc_security),
 	LSM_HOOK_INIT(inode_init_security, smack_inode_init_security),
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 716c92ec941a..f9adddc42ac8 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -63,21 +63,15 @@ static void tomoyo_bprm_committed_creds(struct linux_binprm *bprm)
 
 #ifndef CONFIG_SECURITY_TOMOYO_OMIT_USERSPACE_LOADER
 /**
- * tomoyo_bprm_set_creds - Target for security_bprm_set_creds().
+ * tomoyo_bprm_for_exec - Target for security_bprm_creds_for_exec().
  *
  * @bprm: Pointer to "struct linux_binprm".
  *
  * Returns 0.
  */
-static int tomoyo_bprm_set_creds(struct linux_binprm *bprm)
+static int tomoyo_bprm_creds_for_exec(struct linux_binprm *bprm)
 {
 	/*
-	 * Do only if this function is called for the first time of an execve
-	 * operation.
-	 */
-	if (bprm->called_set_creds)
-		return 0;
-	/*
 	 * Load policy if /sbin/tomoyo-init exists and /sbin/init is requested
 	 * for the first time.
 	 */
@@ -539,7 +533,7 @@ static struct security_hook_list tomoyo_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(task_alloc, tomoyo_task_alloc),
 	LSM_HOOK_INIT(task_free, tomoyo_task_free),
 #ifndef CONFIG_SECURITY_TOMOYO_OMIT_USERSPACE_LOADER
-	LSM_HOOK_INIT(bprm_set_creds, tomoyo_bprm_set_creds),
+	LSM_HOOK_INIT(bprm_creds_for_exec, tomoyo_bprm_creds_for_exec),
 #endif
 	LSM_HOOK_INIT(bprm_check_security, tomoyo_bprm_check_security),
 	LSM_HOOK_INIT(file_fcntl, tomoyo_file_fcntl),