[PATCH v5 10/15] exec: Use secureexec for setting dumpability

From: Kees Cook
Date: Tue Aug 01 2017 - 15:19:04 EST

The examination of "current" to decide dumpability is wrong. This was a
check of and euid/uid (or egid/gid) mismatch in the existing process,
not the newly created one. This appears to stretch back into even the
"history.git" tree. Luckily, dumpability is later set in commit_creds().
In earlier kernel versions before creds existed, similar checks also
existed late in the exec flow, covering up the mistake as far back as I
could find.

Note that because the commit_creds() check examines differences of euid,
uid, egid, gid, and capabilities between the old and new creds, it would
look like the setup_new_exec() dumpability test could be entirely removed.
However, the secureexec test may cover a different set of tests (specific
to the LSMs) than what commit_creds() checks for. So, fix this test to
use secureexec (the removed euid tests are redundant to the commoncap
secureexec checks now).

Cc: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
Reviewed-by: James Morris <james.l.morris@xxxxxxxxxx>
fs/exec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index eca0cb550a06..3536437ffd76 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1354,7 +1354,7 @@ void setup_new_exec(struct linux_binprm * bprm)

current->sas_ss_sp = current->sas_ss_size = 0;

- if (uid_eq(current_euid(), current_uid()) && gid_eq(current_egid(), current_gid()))
+ if (!bprm->secureexec)
set_dumpable(current->mm, SUID_DUMP_USER);
set_dumpable(current->mm, suid_dumpable);