From f34af8e3e3d64f3fc7e7ed2996bdc3858a249b62 Mon Sep 17 00:00:00 2001
From: Paul Moore <paul@paul-moore.com>
Date: Mon, 9 Oct 2023 13:18:49 -0400
Subject: [PATCH] audit: don't take task_lock() in audit_exe_compare() code
path
commit 47846d51348dd62e5231a83be040981b17c955fa upstream.
The get_task_exe_file() function locks the given task with task_lock()
which when used inside audit_exe_compare() can cause deadlocks on
systems that generate audit records when the task_lock() is held. We
resolve this problem with two changes: ignoring those cases where the
task being audited is not the current task, and changing our approach
to obtaining the executable file struct to not require task_lock().
With the intent of the audit exe filter being to filter on audit events
generated by processes started by the specified executable, it makes
sense that we would only want to use the exe filter on audit records
associated with the currently executing process, e.g. @current. If
we are asked to filter records using a non-@current task_struct we can
safely ignore the exe filter without negatively impacting the admin's
expectations for the exe filter.
Knowing that we only have to worry about filtering the currently
executing task in audit_exe_compare() we can do away with the
task_lock() and call get_mm_exe_file() with @current->mm directly.
Cc: <stable@vger.kernel.org>
Fixes: 5efc244346f9 ("audit: fix exe_file access in audit_exe_compare")
Reported-by: Andreas Steinmetz <anstein99@googlemail.com>
Reviewed-by: John Johansen <john.johanse@canonical.com>
Reviewed-by: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/audit_watch.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
index 65075f1e4ac8c..91e82e34b51e3 100644
--- a/kernel/audit_watch.c
+++ b/kernel/audit_watch.c
@@ -527,11 +527,18 @@ int audit_exe_compare(struct task_struct *tsk, struct audit_fsnotify_mark *mark)
unsigned long ino;
dev_t dev;
- exe_file = get_task_exe_file(tsk);
+ /* only do exe filtering if we are recording @current events/records */
+ if (tsk != current)
+ return 0;
+
+ if (WARN_ON_ONCE(!current->mm))
+ return 0;
+ exe_file = get_mm_exe_file(current->mm);
if (!exe_file)
return 0;
ino = file_inode(exe_file)->i_ino;
dev = file_inode(exe_file)->i_sb->s_dev;
fput(exe_file);
+
return audit_mark_compare(mark, ino, dev);
}
--
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