[PATCH][SRU][xenial] apparmor: provide userspace flag indicating binfmt_elf_mmap change

[John Johansen]

Commit 7b8d468e60d6 ("binfmt_elf: switch to new creds when switching to new mm") brought upstream
Commit 9f834ec18def ("binfmt_elf: switch to new creds when switching to new mm")
back to Xenial without the required apparmor flag to indicate the change.

This is a backport of the apparmor fix

Commit 9f834ec18def ("binfmt_elf: switch to new creds when switching to new mm")
changed when the creds are installed by the binfmt_elf handler. This
affects which creds are used to mmap the executable into the address
space. Which can have an affect on apparmor policy.

Add a flag to apparmor at
/sys/kernel/security/apparmor/features/domain/fix_binfmt_elf_mmap

to make it possible to detect this semantic change so that the userspace
tools and the regression test suite can correctly deal with the change.

BugLink: http://bugs.launchpad.net/bugs/1630069
Signed-off-by: John Johansen <john.johansen at canonical.com>
(backported from commit 34c426acb75cc21bdf84685e106db0c1a3565057)
---
 security/apparmor/apparmorfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 6950d27105e6..f63fa9a4f25d 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -1533,6 +1533,7 @@ static struct aa_fs_entry aa_fs_entry_domain[] = {
 	AA_FS_FILE_BOOLEAN("change_profile",	1),
 	AA_FS_FILE_BOOLEAN("stack",		1),
 	AA_FS_FILE_STRING("version", "1.2"),
+	AA_FS_FILE_BOOLEAN("fix_binfmt_elf_mmap",	1),
 	{ }
 };
 
-- 
2.17.1