linux-hardening - [PATCH] apparmor: aa_buffer: Convert 1-element array to flexible array

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Date:   Thu, 11 May 2023 14:34:45 -0700
From:   Kees Cook <keescook@...omium.org>
To:     John Johansen <john.johansen@...onical.com>
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, apparmor@...ts.ubuntu.com,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] apparmor: aa_buffer: Convert 1-element array to flexible array

In the ongoing effort to convert all fake flexible arrays to proper
flexible arrays, replace aa_buffer's 1-element "buffer" member with a
flexible array.

Cc: John Johansen <john.johansen@...onical.com>
Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
Cc: Paul Moore <paul@...l-moore.com>
Cc: James Morris <jmorris@...ei.org>
Cc: "Serge E. Hallyn" <serge@...lyn.com>
Cc: apparmor@...ts.ubuntu.com
Cc: linux-security-module@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
One thing I notice here is that it may be rare for "buffer" to ever change
for a given kernel. Could this just be made PATH_MAX * 2 directly and
remove the module parameter, etc, etc?
---
 security/apparmor/lsm.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index d6cc4812ca53..35eb41bb9e3a 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -46,7 +46,7 @@ int apparmor_initialized;
 
 union aa_buffer {
 	struct list_head list;
-	char buffer[1];
+	DECLARE_FLEX_ARRAY(char, buffer);
 };
 
 #define RESERVE_COUNT 2
@@ -1647,7 +1647,7 @@ char *aa_get_buffer(bool in_atomic)
 		list_del(&aa_buf->list);
 		buffer_count--;
 		spin_unlock(&aa_buffers_lock);
-		return &aa_buf->buffer[0];
+		return aa_buf->buffer;
 	}
 	if (in_atomic) {
 		/*
@@ -1670,7 +1670,7 @@ char *aa_get_buffer(bool in_atomic)
 		pr_warn_once("AppArmor: Failed to allocate a memory buffer.\n");
 		return NULL;
 	}
-	return &aa_buf->buffer[0];
+	return aa_buf->buffer;
 }
 
 void aa_put_buffer(char *buf)
@@ -1747,7 +1747,7 @@ static int __init alloc_buffers(void)
 			destroy_buffers();
 			return -ENOMEM;
 		}
-		aa_put_buffer(&aa_buf->buffer[0]);
+		aa_put_buffer(aa_buf->buffer);
 	}
 	return 0;
 }
-- 
2.34.1