[PATCH RFC 2/4] process: add the PF_SUID flag

From: Wander Lairson Costa
Date: Mon Dec 27 2021 - 17:37:04 EST


If the binary file in an execve system call is a suid executable, we add
the PF_SUID flag to the process and all its future new children and
threads.

In a later commit, we will use this information to determine if it is
safe to core dump such a process.

Signed-off-by: Wander Lairson Costa <wander@xxxxxxxxxx>
---
fs/exec.c | 4 ++++
include/linux/sched.h | 1 +
kernel/fork.c | 2 ++
3 files changed, 7 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index 3913b335b95f..b4bd157a5282 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1311,6 +1311,10 @@ int begin_new_exec(struct linux_binprm * bprm)

me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
PF_NOFREEZE | PF_NO_SETAFFINITY);
+
+ if (bprm->suid_bin)
+ me->flags |= PF_SUID;
+
flush_thread();
me->personality &= ~bprm->per_clear;

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e3b328b81ac0..f7811c42b004 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1651,6 +1651,7 @@ extern struct pid *cad_pid;
#define PF_VCPU 0x00000001 /* I'm a virtual CPU */
#define PF_IDLE 0x00000002 /* I am an IDLE thread */
#define PF_EXITING 0x00000004 /* Getting shut down */
+#define PF_SUID 0x00000008 /* The process comes from a suid/sgid binary */
#define PF_IO_WORKER 0x00000010 /* Task is an IO worker */
#define PF_WQ_WORKER 0x00000020 /* I'm a workqueue worker */
#define PF_FORKNOEXEC 0x00000040 /* Forked but didn't exec */
diff --git a/kernel/fork.c b/kernel/fork.c
index 231b1ba3ca9f..1e1ffff70d14 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2080,6 +2080,8 @@ static __latent_entropy struct task_struct *copy_process(
delayacct_tsk_init(p); /* Must remain after dup_task_struct() */
p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE | PF_NO_SETAFFINITY);
p->flags |= PF_FORKNOEXEC;
+ if (current->flags & PF_SUID)
+ p->flags |= PF_SUID;
INIT_LIST_HEAD(&p->children);
INIT_LIST_HEAD(&p->sibling);
rcu_copy_process(p);
--
2.27.0