kernel: Only expose su when daemon is running

It has been claimed that the PG implementation of 'su' has security
vulnerabilities even when disabled.  Unfortunately, the people that
find these vulnerabilities often like to keep them private so they
can profit from exploits while leaving users exposed to malicious
hackers.

In order to reduce the attack surface for vulnerabilites, it is
therefore necessary to make 'su' completely inaccessible when it
is not in use (except by the root and system users).

Change-Id: I79716c72f74d0b7af34ec3a8054896c6559a181d

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 240a38eeb..e8a3ee5dd 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1572,6 +1572,11 @@ static int do_execve_common(const char *filename,
 	if (retval < 0)
 		goto out;
 
+	if (d_is_su(file->f_dentry) && capable(CAP_SYS_ADMIN)) {
+		current->flags |= PF_SU;
+		su_exec();
+	}
+
 	/* execve succeeded */
 	current->fs->in_exec = 0;
 	current->in_execve = 0;