linux-kernel - [PATCH RFC v2 2/4] process: add the PF

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Message-Id: <20211228170910.623156-3-wander@redhat.com>
Date:   Tue, 28 Dec 2021 14:09:06 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Laurent Vivier <laurent@...ier.eu>,
        YunQiang Su <ysu@...ecomp.com>, Helge Deller <deller@....de>,
        Wander Lairson Costa <wander@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexey Gladkov <legion@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Rolf Eike Beer <eb@...ix.com>,
        linux-fsdevel@...r.kernel.org (open list:FILESYSTEMS (VFS and
        infrastructure)), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH RFC v2 2/4] process: add the PF_SUID flag

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@...hat.com>
---
 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 ec07b36fdbb4..81d6ab9a4f64 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1309,6 +1309,10 @@ 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 78c351e35fec..8ec2f907fb89 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1683,6 +1683,7 @@ extern struct pid *cad_pid;
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
 #define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
+#define PF_SUID			0x01000000	/* The process comes from a suid/sgid binary */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
 #define PF_MEMALLOC_PIN		0x10000000	/* Allocation context constrained to zones which allow long term pinning. */
diff --git a/kernel/fork.c b/kernel/fork.c
index 3244cc56b697..f0375d102b57 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2076,6 +2076,8 @@ 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