Implement kernel_execve

This set of changes implements kernel_execve to remove the need for
kernel threads to pass in pointers to in-kernel data structures
to functions that take __user pointers.   Which is part of the
greater removal of set_fs work.

This set of changes makes do_execve static and so I have updated the
comments.  This affects the comments in the x86 entry point code
and the comments in tomoyo.  I believe I have updated them correctly.
If not please let me know.

I have moved the calls of copy_strings before the call of
security_bprm_creds_for_exec.  Which might be of interest to the
security folks.  I can't see that it matters but I have copied the
security folks just to be certain.

By moving the initialization of the new stack that copy_strings does
earlier it becomes possible to copy all of the parameters to exec before
anything else is done which makes it possible to have one function
kernel_execve that uncondtionally handles copying parameters from kernel
space, and another function do_execveat_common which handles copying
parameters from userspace.

This work was inspired by Christoph Hellwig's similar patchset, which my
earlier work to remove the file parameter to do_execveat_common
conflicted with.
https://lore.kernel.org/linux-fsdevel/20200627072704.2447163-1-hch@lst.de/

I figured that after causing all of that trouble for the set_fs work
the least I could do is implement the change myself.

The big practical change from Christoph's work is that he did not
separate out the copying of parameters from the rest of the work of
exec, which did not help the maintainability of the code.

Eric W. Biederman (7):
      exec: Remove unnecessary spaces from binfmts.h
      exec: Factor out alloc_bprm
      exec: Move initialization of bprm->filename into alloc_bprm
      exec: Move bprm_mm_init into alloc_bprm
      exec: Factor bprm_execve out of do_execve_common
      exec: Factor bprm_stack_limits out of prepare_arg_pages
      exec: Implement kernel_execve

 arch/x86/entry/entry_32.S      |   2 +-
 arch/x86/entry/entry_64.S      |   2 +-
 arch/x86/kernel/unwind_frame.c |   2 +-
 fs/exec.c                      | 301 ++++++++++++++++++++++++++++-------------
 include/linux/binfmts.h        |  20 ++-
 init/main.c                    |   4 +-
 kernel/umh.c                   |   6 +-
 security/tomoyo/common.h       |   2 +-
 security/tomoyo/domain.c       |   4 +-
 security/tomoyo/tomoyo.c       |   4 +-
 10 files changed, 224 insertions(+), 123 deletions(-)

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/871rle8bw2.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

3 files changed, 5 insertions, 5 deletions

diff --git a/security/tomoyo/common.h b/security/tomoyo/common.h
index 050473df5809..85246b9df7ca 100644
--- a/security/tomoyo/common.h
+++ b/security/tomoyo/common.h
@@ -425,7 +425,7 @@ struct tomoyo_request_info {
 	struct tomoyo_obj_info *obj;
 	/*
 	 * For holding parameters specific to execve() request.
-	 * NULL if not dealing do_execve().
+	 * NULL if not dealing execve().
 	 */
 	struct tomoyo_execve *ee;
 	struct tomoyo_domain_info *domain;
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index 7869d6a9980b..53b3e1f5f227 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -767,7 +767,7 @@ retry:
 
 	/*
 	 * Check for domain transition preference if "file execute" matched.
-	 * If preference is given, make do_execve() fail if domain transition
+	 * If preference is given, make execve() fail if domain transition
 	 * has failed, for domain transition preference should be used with
 	 * destination domain defined.
 	 */
@@ -810,7 +810,7 @@ force_reset_domain:
 		snprintf(ee->tmp, TOMOYO_EXEC_TMPSIZE - 1, "<%s>",
 			 candidate->name);
 		/*
-		 * Make do_execve() fail if domain transition across namespaces
+		 * Make execve() fail if domain transition across namespaces
 		 * has failed.
 		 */
 		reject_on_transition_failure = true;
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index f9adddc42ac8..1f3cd432d830 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -93,7 +93,7 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
 	struct tomoyo_task *s = tomoyo_task(current);
 
 	/*
-	 * Execute permission is checked against pathname passed to do_execve()
+	 * Execute permission is checked against pathname passed to execve()
 	 * using current domain.
 	 */
 	if (!s->old_domain_info) {
@@ -307,7 +307,7 @@ static int tomoyo_file_fcntl(struct file *file, unsigned int cmd,
  */
 static int tomoyo_file_open(struct file *f)
 {
-	/* Don't check read permission here if called from do_execve(). */
+	/* Don't check read permission here if called from execve(). */
 	if (current->in_execve)
 		return 0;
 	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,