procfs: block chmod on /proc/thread-self/comm

JIRA: https://issues.redhat.com/browse/RHEL-105165

commit ccf6148
Author: Aleksa Sarai <cyphar@cyphar.com>
Date:   Fri, 14 Jul 2023 00:09:58 +1000

    procfs: block chmod on /proc/thread-self/comm

    Due to an oversight in commit 1b3044e ("procfs: fix pthread
    cross-thread naming if !PR_DUMPABLE") in switching from REG to NOD,
    chmod operations on /proc/thread-self/comm were no longer blocked as
    they are on almost all other procfs files.

    A very similar situation with /proc/self/environ was used to as a root
    exploit a long time ago, but procfs has SB_I_NOEXEC so this is simply a
    correctness issue.

    Ref: https://lwn.net/Articles/191954/
    Ref: 6d76fa5 ("Don't allow chmod() on the /proc/<pid>/ files")
    Fixes: 1b3044e ("procfs: fix pthread cross-thread naming if !PR_DUMPABLE")
    Cc: stable@vger.kernel.org # v4.7+
    Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
    Message-Id: <20230713141001.27046-1-cyphar@cyphar.com>
    Signed-off-by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

fs/proc/base.c

@@ -3555,7 +3555,8 @@ static int proc_tid_comm_permission(struct mnt_idmap *idmap,
 }
 
 static const struct inode_operations proc_tid_comm_inode_operations = {
-		.permission = proc_tid_comm_permission,
+		.setattr	= proc_setattr,
+		.permission	= proc_tid_comm_permission,
 };
 
 /*