exec: Remove the recomputation of bprm->cred

Recomputing the uids, gids, capabilities, and related flags each time a
new bprm->file is set is error prone and unnecessary.

This set of changes splits per_clear temporarily into two separate
variables.  This is the last change necessary to ensure that
everything that is computed from brpm->file in bprm->cred is
recomputed every time a new bprm->file is set.  Then the code is
refactored to compute bprm->cred from bprm->file when the final
brpm->file is known, removing the need for recomputation entirely.

Doing this in two steps should allow anyone who has problems later to
bisect and tell if it was the semantic change or the refactoring that
caused them problems.

Eric W. Biederman (2):
      exec: Add a per bprm->file version of per_clear
      exec: Compute file based creds only once

 fs/binfmt_misc.c              |  2 +-
 fs/exec.c                     | 57 ++++++++++++++++++-------------------------
 include/linux/binfmts.h       |  9 ++-----
 include/linux/lsm_hook_defs.h |  2 +-
 include/linux/lsm_hooks.h     | 22 +++++++++--------
 include/linux/security.h      |  9 ++++---
 security/commoncap.c          | 22 +++++++++--------
 security/security.c           |  4 +--
 8 files changed, 59 insertions(+), 68 deletions(-)

Merge branch 'exec-norecompute-v2' into exec-next

2 files changed, 14 insertions, 12 deletions

diff --git a/security/commoncap.c b/security/commoncap.c
index 77b04cb6feac..59bf3c1674c8 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -647,7 +647,8 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
  * its xattrs and, if present, apply them to the proposed credentials being
  * constructed by execve().
  */
-static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_fcap)
+static int get_file_caps(struct linux_binprm *bprm, struct file *file,
+			 bool *effective, bool *has_fcap)
 {
 	int rc = 0;
 	struct cpu_vfs_cap_data vcaps;
@@ -657,7 +658,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_f
 	if (!file_caps_enabled)
 		return 0;
 
-	if (!mnt_may_suid(bprm->file->f_path.mnt))
+	if (!mnt_may_suid(file->f_path.mnt))
 		return 0;
 
 	/*
@@ -665,10 +666,10 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_f
 	 * explicit that capability bits are limited to s_user_ns and its
 	 * descendants.
 	 */
-	if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
+	if (!current_in_userns(file->f_path.mnt->mnt_sb->s_user_ns))
 		return 0;
 
-	rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
+	rc = get_vfs_caps_from_disk(file->f_path.dentry, &vcaps);
 	if (rc < 0) {
 		if (rc == -EINVAL)
 			printk(KERN_NOTICE "Invalid argument reading file caps for %s\n",
@@ -797,26 +798,27 @@ static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old,
 }
 
 /**
- * cap_bprm_repopulate_creds - Set up the proposed credentials for execve().
+ * cap_bprm_creds_from_file - Set up the proposed credentials for execve().
  * @bprm: The execution parameters, including the proposed creds
+ * @file: The file to pull the credentials from
  *
  * Set up the proposed credentials for a new execution context being
  * constructed by execve().  The proposed creds in @bprm->cred is altered,
  * which won't take effect immediately.  Returns 0 if successful, -ve on error.
  */
-int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
+int cap_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file)
 {
+	/* Process setpcap binaries and capabilities for uid 0 */
 	const struct cred *old = current_cred();
 	struct cred *new = bprm->cred;
 	bool effective = false, has_fcap = false, is_setid;
 	int ret;
 	kuid_t root_uid;
 
-	new->cap_ambient = old->cap_ambient;
 	if (WARN_ON(!cap_ambient_invariant_ok(old)))
 		return -EPERM;
 
-	ret = get_file_caps(bprm, &effective, &has_fcap);
+	ret = get_file_caps(bprm, file, &effective, &has_fcap);
 	if (ret < 0)
 		return ret;
 
@@ -889,7 +891,7 @@ int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
 	    (!__is_real(root_uid, new) &&
 	     (effective ||
 	      __cap_grew(permitted, ambient, new))))
-		bprm->active_secureexec = 1;
+		bprm->secureexec = 1;
 
 	return 0;
 }
@@ -1346,7 +1348,7 @@ static struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme),
 	LSM_HOOK_INIT(capget, cap_capget),
 	LSM_HOOK_INIT(capset, cap_capset),
-	LSM_HOOK_INIT(bprm_repopulate_creds, cap_bprm_repopulate_creds),
+	LSM_HOOK_INIT(bprm_creds_from_file, cap_bprm_creds_from_file),
 	LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
 	LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
 	LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),
diff --git a/security/security.c b/security/security.c
index b890b7e2a765..259b8e750aa2 100644
--- a/security/security.c
+++ b/security/security.c
@@ -828,9 +828,9 @@ int security_bprm_creds_for_exec(struct linux_binprm *bprm)
 	return call_int_hook(bprm_creds_for_exec, 0, bprm);
 }
 
-int security_bprm_repopulate_creds(struct linux_binprm *bprm)
+int security_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file)
 {
-	return call_int_hook(bprm_repopulate_creds, 0, bprm);
+	return call_int_hook(bprm_creds_from_file, 0, bprm, file);
 }
 
 int security_bprm_check(struct linux_binprm *bprm)