Merge tag 'secureexec-v4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull secureexec update from Kees Cook:
 "This series has the ultimate goal of providing a sane stack rlimit
  when running set*id processes.

  To do this, the bprm_secureexec LSM hook is collapsed into the
  bprm_set_creds hook so the secureexec-ness of an exec can be
  determined early enough to make decisions about rlimits and the
  resulting memory layouts. Other logic acting on the secureexec-ness of
  an exec is similarly consolidated. Capabilities needed some special
  handling, but the refactoring removed other special handling, so that
  was a wash"

* tag 'secureexec-v4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  exec: Consolidate pdeath_signal clearing
  exec: Use sane stack rlimit under secureexec
  exec: Consolidate dumpability logic
  smack: Remove redundant pdeath_signal clearing
  exec: Use secureexec for clearing pdeath_signal
  exec: Use secureexec for setting dumpability
  LSM: drop bprm_secureexec hook
  commoncap: Move cap_elevated calculation into bprm_set_creds
  commoncap: Refactor to remove bprm_secureexec hook
  smack: Refactor to remove bprm_secureexec hook
  selinux: Refactor to remove bprm_secureexec hook
  apparmor: Refactor to remove bprm_secureexec hook
  binfmt: Introduce secureexec flag
  exec: Correct comments about "point of no return"
  exec: Rename bprm->cred_prepared to called_set_creds

Author: torvalds

fs/binfmt_elf.c

@@ -252,7 +252,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
 	NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid));
 	NEW_AUX_ENT(AT_GID, from_kgid_munged(cred->user_ns, cred->gid));
 	NEW_AUX_ENT(AT_EGID, from_kgid_munged(cred->user_ns, cred->egid));
- 	NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+	NEW_AUX_ENT(AT_SECURE, bprm->secureexec);
 	NEW_AUX_ENT(AT_RANDOM, (elf_addr_t)(unsigned long)u_rand_bytes);
 #ifdef ELF_HWCAP2
 	NEW_AUX_ENT(AT_HWCAP2, ELF_HWCAP2);

fs/binfmt_elf_fdpic.c

@@ -650,7 +650,7 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
 	NEW_AUX_ENT(AT_EUID,	(elf_addr_t) from_kuid_munged(cred->user_ns, cred->euid));
 	NEW_AUX_ENT(AT_GID,	(elf_addr_t) from_kgid_munged(cred->user_ns, cred->gid));
 	NEW_AUX_ENT(AT_EGID,	(elf_addr_t) from_kgid_munged(cred->user_ns, cred->egid));
-	NEW_AUX_ENT(AT_SECURE,	security_bprm_secureexec(bprm));
+	NEW_AUX_ENT(AT_SECURE,	bprm->secureexec);
 	NEW_AUX_ENT(AT_EXECFN,	bprm->exec);
 
 #ifdef ARCH_DLINFO

fs/binfmt_flat.c

@@ -890,7 +890,7 @@ static int load_flat_shared_library(int id, struct lib_info *libs)
 	 * as we're past the point of no return and are dealing with shared
 	 * libraries.
 	 */
-	bprm.cred_prepared = 1;
+	bprm.called_set_creds = 1;
 
 	res = prepare_binprm(&bprm);
 

fs/exec.c

@@ -1259,6 +1259,12 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
 	perf_event_comm(tsk, exec);
 }
 
+/*
+ * Calling this is the point of no return. None of the failures will be
+ * seen by userspace since either the process is already taking a fatal
+ * signal (via de_thread() or coredump), or will have SEGV raised
+ * (after exec_mmap()) by search_binary_handlers (see below).
+ */
 int flush_old_exec(struct linux_binprm * bprm)
 {
 	int retval;
@@ -1286,7 +1292,13 @@ int flush_old_exec(struct linux_binprm * bprm)
 	if (retval)
 		goto out;
 
-	bprm->mm = NULL;		/* We're using it now */
+	/*
+	 * After clearing bprm->mm (to mark that current is using the
+	 * prepared mm now), we have nothing left of the original
+	 * process. If anything from here on returns an error, the check
+	 * in search_binary_handler() will SEGV current.
+	 */
+	bprm->mm = NULL;
 
 	set_fs(USER_DS);
 	current->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
@@ -1331,15 +1343,38 @@ EXPORT_SYMBOL(would_dump);
 
 void setup_new_exec(struct linux_binprm * bprm)
 {
+	/*
+	 * Once here, prepare_binrpm() will not be called any more, so
+	 * the final state of setuid/setgid/fscaps can be merged into the
+	 * secureexec flag.
+	 */
+	bprm->secureexec |= bprm->cap_elevated;
+
+	if (bprm->secureexec) {
+		/* Make sure parent cannot signal privileged process. */
+		current->pdeath_signal = 0;
+
+		/*
+		 * For secureexec, reset the stack limit to sane default to
+		 * avoid bad behavior from the prior rlimits. This has to
+		 * happen before arch_pick_mmap_layout(), which examines
+		 * RLIMIT_STACK, but after the point of no return to avoid
+		 * needing to clean up the change on failure.
+		 */
+		if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM)
+			current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM;
+	}
+
 	arch_pick_mmap_layout(current->mm);
 
-	/* This is the point of no return */
 	current->sas_ss_sp = current->sas_ss_size = 0;
 
-	if (uid_eq(current_euid(), current_uid()) && gid_eq(current_egid(), current_gid()))
-		set_dumpable(current->mm, SUID_DUMP_USER);
-	else
+	/* Figure out dumpability. */
+	if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP ||
+	    bprm->secureexec)
 		set_dumpable(current->mm, suid_dumpable);
+	else
+		set_dumpable(current->mm, SUID_DUMP_USER);
 
 	arch_setup_new_exec();
 	perf_event_exec();
@@ -1351,15 +1386,6 @@ void setup_new_exec(struct linux_binprm * bprm)
 	 */
 	current->mm->task_size = TASK_SIZE;
 
-	/* install the new credentials */
-	if (!uid_eq(bprm->cred->uid, current_euid()) ||
-	    !gid_eq(bprm->cred->gid, current_egid())) {
-		current->pdeath_signal = 0;
-	} else {
-		if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)
-			set_dumpable(current->mm, suid_dumpable);
-	}
-
 	/* An exec changes our domain. We are no longer part of the thread
 	   group */
 	current->self_exec_id++;
@@ -1548,7 +1574,7 @@ int prepare_binprm(struct linux_binprm *bprm)
 	retval = security_bprm_set_creds(bprm);
 	if (retval)
 		return retval;
-	bprm->cred_prepared = 1;
+	bprm->called_set_creds = 1;
 
 	memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 	return kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);

include/linux/binfmts.h

@@ -25,11 +25,25 @@ struct linux_binprm {
 	struct mm_struct *mm;
 	unsigned long p; /* current top of mem */
 	unsigned int
-		cred_prepared:1,/* true if creds already prepared (multiple
-				 * preps happen for interpreters) */
-		cap_effective:1;/* true if has elevated effective capabilities,
-				 * false if not; except for init which inherits
-				 * its parent's caps anyway */
+		/*
+		 * True after the bprm_set_creds hook has been called once
+		 * (multiple calls can be made via prepare_binprm() for
+		 * binfmt_script/misc).
+		 */
+		called_set_creds:1,
+		/*
+		 * True if most recent call to the commoncaps bprm_set_creds
+		 * hook (due to multiple prepare_binprm() calls from the
+		 * binfmt_script/misc handlers) resulted in elevated
+		 * privileges.
+		 */
+		cap_elevated:1,
+		/*
+		 * Set by bprm_set_creds hook to indicate a privilege-gaining
+		 * exec has happened. Used to sanitize execution environment
+		 * and to set AT_SECURE auxv for glibc.
+		 */
+		secureexec:1;
 #ifdef __alpha__
 	unsigned int taso:1;
 #endif

include/linux/lsm_hooks.h

@@ -43,7 +43,11 @@
  *	interpreters.  The hook can tell whether it has already been called by
  *	checking to see if @bprm->security is non-NULL.  If so, then the hook
  *	may decide either to retain the security information saved earlier or
- *	to replace it.
+ *	to replace it.  The hook must set @bprm->secureexec to 1 if a "secure
+ *	exec" has happened as a result of this hook call.  The flag is used to
+ *	indicate the need for a sanitized execution environment, and is also
+ *	passed in the ELF auxiliary table on the initial stack to indicate
+ *	whether libc should enable secure mode.
  *	@bprm contains the linux_binprm structure.
  *	Return 0 if the hook is successful and permission is granted.
  * @bprm_check_security:
@@ -71,12 +75,6 @@
  *	linux_binprm structure.  This hook is a good place to perform state
  *	changes on the process such as clearing out non-inheritable signal
  *	state.  This is called immediately after commit_creds().
- * @bprm_secureexec:
- *	Return a boolean value (0 or 1) indicating whether a "secure exec"
- *	is required.  The flag is passed in the auxiliary table
- *	on the initial stack to the ELF interpreter to indicate whether libc
- *	should enable secure mode.
- *	@bprm contains the linux_binprm structure.
  *
  * Security hooks for filesystem operations.
  *
@@ -1388,7 +1386,6 @@ union security_list_options {
 
 	int (*bprm_set_creds)(struct linux_binprm *bprm);
 	int (*bprm_check_security)(struct linux_binprm *bprm);
-	int (*bprm_secureexec)(struct linux_binprm *bprm);
 	void (*bprm_committing_creds)(struct linux_binprm *bprm);
 	void (*bprm_committed_creds)(struct linux_binprm *bprm);
 
@@ -1710,7 +1707,6 @@ struct security_hook_heads {
 	struct list_head vm_enough_memory;
 	struct list_head bprm_set_creds;
 	struct list_head bprm_check_security;
-	struct list_head bprm_secureexec;
 	struct list_head bprm_committing_creds;
 	struct list_head bprm_committed_creds;
 	struct list_head sb_alloc_security;

include/linux/security.h

@@ -85,7 +85,6 @@ extern int cap_capset(struct cred *new, const struct cred *old,
 		      const kernel_cap_t *inheritable,
 		      const kernel_cap_t *permitted);
 extern int cap_bprm_set_creds(struct linux_binprm *bprm);
-extern int cap_bprm_secureexec(struct linux_binprm *bprm);
 extern int cap_inode_setxattr(struct dentry *dentry, const char *name,
 			      const void *value, size_t size, int flags);
 extern int cap_inode_removexattr(struct dentry *dentry, const char *name);
@@ -232,7 +231,6 @@ int security_bprm_set_creds(struct linux_binprm *bprm);
 int security_bprm_check(struct linux_binprm *bprm);
 void security_bprm_committing_creds(struct linux_binprm *bprm);
 void security_bprm_committed_creds(struct linux_binprm *bprm);
-int security_bprm_secureexec(struct linux_binprm *bprm);
 int security_sb_alloc(struct super_block *sb);
 void security_sb_free(struct super_block *sb);
 int security_sb_copy_data(char *orig, char *copy);
@@ -541,11 +539,6 @@ static inline void security_bprm_committed_creds(struct linux_binprm *bprm)
 {
 }
 
-static inline int security_bprm_secureexec(struct linux_binprm *bprm)
-{
-	return cap_bprm_secureexec(bprm);
-}
-
 static inline int security_sb_alloc(struct super_block *sb)
 {
 	return 0;

security/apparmor/domain.c

@@ -758,7 +758,7 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 		file_inode(bprm->file)->i_mode
 	};
 
-	if (bprm->cred_prepared)
+	if (bprm->called_set_creds)
 		return 0;
 
 	ctx = cred_ctx(bprm->cred);
@@ -807,7 +807,7 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 			aa_label_printk(new, GFP_ATOMIC);
 			dbg_printk("\n");
 		}
-		bprm->unsafe |= AA_SECURE_X_NEEDED;
+		bprm->secureexec = 1;
 	}
 
 	if (label->proxy != new->proxy) {
@@ -843,23 +843,6 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 	goto done;
 }
 
-/**
- * apparmor_bprm_secureexec - determine if secureexec is needed
- * @bprm: binprm for exec  (NOT NULL)
- *
- * Returns: %1 if secureexec is needed else %0
- */
-int apparmor_bprm_secureexec(struct linux_binprm *bprm)
-{
-	/* the decision to use secure exec is computed in set_creds
-	 * and stored in bprm->unsafe.
-	 */
-	if (bprm->unsafe & AA_SECURE_X_NEEDED)
-		return 1;
-
-	return 0;
-}
-
 /*
  * Functions for self directed profile change
  */

security/apparmor/include/domain.h

@@ -30,7 +30,6 @@ struct aa_domain {
 #define AA_CHANGE_STACK 8
 
 int apparmor_bprm_set_creds(struct linux_binprm *bprm);
-int apparmor_bprm_secureexec(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);

security/apparmor/include/file.h

@@ -101,9 +101,6 @@ static inline struct aa_label *aa_get_file_label(struct aa_file_ctx *ctx)
 #define AA_X_INHERIT		0x4000
 #define AA_X_UNCONFINED		0x8000
 
-/* AA_SECURE_X_NEEDED - is passed in the bprm->unsafe field */
-#define AA_SECURE_X_NEEDED	0x8000
-
 /* need to make conditional which ones are being set */
 struct path_cond {
 	kuid_t uid;

security/apparmor/lsm.c

@@ -694,7 +694,6 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(bprm_set_creds, apparmor_bprm_set_creds),
 	LSM_HOOK_INIT(bprm_committing_creds, apparmor_bprm_committing_creds),
 	LSM_HOOK_INIT(bprm_committed_creds, apparmor_bprm_committed_creds),
-	LSM_HOOK_INIT(bprm_secureexec, apparmor_bprm_secureexec),
 
 	LSM_HOOK_INIT(task_setrlimit, apparmor_task_setrlimit),
 };

security/commoncap.c

@@ -285,15 +285,6 @@ int cap_capset(struct cred *new,
 	return 0;
 }
 
-/*
- * Clear proposed capability sets for execve().
- */
-static inline void bprm_clear_caps(struct linux_binprm *bprm)
-{
-	cap_clear(bprm->cred->cap_permitted);
-	bprm->cap_effective = false;
-}
-
 /**
  * cap_inode_need_killpriv - Determine if inode change affects privileges
  * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
@@ -443,7 +434,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
 	int rc = 0;
 	struct cpu_vfs_cap_data vcaps;
 
-	bprm_clear_caps(bprm);
+	cap_clear(bprm->cred->cap_permitted);
 
 	if (!file_caps_enabled)
 		return 0;
@@ -476,7 +467,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
 
 out:
 	if (rc)
-		bprm_clear_caps(bprm);
+		cap_clear(bprm->cred->cap_permitted);
 
 	return rc;
 }
@@ -585,8 +576,6 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
 	if (WARN_ON(!cap_ambient_invariant_ok(new)))
 		return -EPERM;
 
-	bprm->cap_effective = effective;
-
 	/*
 	 * Audit candidate if current->cap_effective is set
 	 *
@@ -614,33 +603,17 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
 	if (WARN_ON(!cap_ambient_invariant_ok(new)))
 		return -EPERM;
 
-	return 0;
-}
-
-/**
- * cap_bprm_secureexec - Determine whether a secure execution is required
- * @bprm: The execution parameters
- *
- * Determine whether a secure execution is required, return 1 if it is, and 0
- * if it is not.
- *
- * The credentials have been committed by this point, and so are no longer
- * available through @bprm->cred.
- */
-int cap_bprm_secureexec(struct linux_binprm *bprm)
-{
-	const struct cred *cred = current_cred();
-	kuid_t root_uid = make_kuid(cred->user_ns, 0);
-
-	if (!uid_eq(cred->uid, root_uid)) {
-		if (bprm->cap_effective)
-			return 1;
-		if (!cap_issubset(cred->cap_permitted, cred->cap_ambient))
-			return 1;
+	/* Check for privilege-elevated exec. */
+	bprm->cap_elevated = 0;
+	if (is_setid) {
+		bprm->cap_elevated = 1;
+	} else if (!uid_eq(new->uid, root_uid)) {
+		if (effective ||
+		    !cap_issubset(new->cap_permitted, new->cap_ambient))
+			bprm->cap_elevated = 1;
 	}
 
-	return (!uid_eq(cred->euid, cred->uid) ||
-		!gid_eq(cred->egid, cred->gid));
+	return 0;
 }
 
 /**
@@ -1079,7 +1052,6 @@ struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(capget, cap_capget),
 	LSM_HOOK_INIT(capset, cap_capset),
 	LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds),
-	LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec),
 	LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
 	LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
 	LSM_HOOK_INIT(mmap_addr, cap_mmap_addr),

security/security.c

@@ -351,11 +351,6 @@ void security_bprm_committed_creds(struct linux_binprm *bprm)
 	call_void_hook(bprm_committed_creds, bprm);
 }
 
-int security_bprm_secureexec(struct linux_binprm *bprm)
-{
-	return call_int_hook(bprm_secureexec, 0, bprm);
-}
-
 int security_sb_alloc(struct super_block *sb)
 {
 	return call_int_hook(sb_alloc_security, 0, sb);