exec: Control flow simplifications

It is hard to follow the control flow in exec.c as the code has evolved over
time and something that used to work one way now works another.  This set of
changes attempts to address the worst of that, to remove unnecessary work
and to make the code a little easier to follow.

The churn is a bit higher than the last version of this patchset, with
renaming and cleaning up of comments.  I have split security_bprm_set_creds
into security_bprm_creds_for_exec and security_bprm_repopulate_creds.  My
goal was to make it clear that one hook completes its work while the other
recaculates it's work each time a new interpreter is selected.

I have added a new change at the beginning to make it clear that neither
security_bprm_creds_for_exec nor security_bprm_repopulate_creds needs to be
implemented as prepare_exec_creds properly does the work of setting up
credentials unless something special is going on.

I have made the execfd support generic and moved out of binfmt_misc so that
I can remove the recursion.

I have moved reassigning bprm->file into the loop that replaces the
recursion.  In doing so I discovered that binfmt_misc was naughty and
was returning -ENOEXEC in such a way that the search_binary_handler loop
could not continue.  So I added a change to remove that naughtiness.

Eric W. Biederman (8):
      exec: Teach prepare_exec_creds how exec treats uids & gids
      exec: Factor security_bprm_creds_for_exec out of security_bprm_set_creds
      exec: Convert security_bprm_set_creds into security_bprm_repopulate_creds
      exec: Allow load_misc_binary to call prepare_binfmt unconditionally
      exec: Move the call of prepare_binprm into search_binary_handler
      exec/binfmt_script: Don't modify bprm->buf and then return -ENOEXEC
      exec: Generic execfd support
      exec: Remove recursion from search_binary_handler

 arch/alpha/kernel/binfmt_loader.c  | 11 +----
 fs/binfmt_elf.c                    |  4 +-
 fs/binfmt_elf_fdpic.c              |  4 +-
 fs/binfmt_em86.c                   | 13 +----
 fs/binfmt_misc.c                   | 69 ++++-----------------------
 fs/binfmt_script.c                 | 82 ++++++++++++++------------------
 fs/exec.c                          | 97 ++++++++++++++++++++++++++------------
 include/linux/binfmts.h            | 36 ++++++--------
 include/linux/lsm_hook_defs.h      |  3 +-
 include/linux/lsm_hooks.h          | 52 +++++++++++---------
 include/linux/security.h           | 14 ++++--
 kernel/cred.c                      |  3 ++
 security/apparmor/domain.c         |  7 +--
 security/apparmor/include/domain.h |  2 +-
 security/apparmor/lsm.c            |  2 +-
 security/commoncap.c               |  9 ++--
 security/security.c                |  9 +++-
 security/selinux/hooks.c           |  8 ++--
 security/smack/smack_lsm.c         |  9 ++--
 security/tomoyo/tomoyo.c           | 12 ++---
 20 files changed, 202 insertions(+), 244 deletions(-)

Link: https://lkml.kernel.org/r/877dx822er.fsf_-_@x220.int.ebiederm.org
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 3 insertions, 5 deletions

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),