linux-hardening - [PATCH 3/4] xattr: Use dedicated slab buckets for setxattr()

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Date: Mon,  4 Mar 2024 10:49:31 -0800
From: Kees Cook <keescook@...omium.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Kees Cook <keescook@...omium.org>,
	Christian Brauner <brauner@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org,
	"GONG, Ruiqi" <gongruiqi@...weicloud.com>,
	Xiu Jianfeng <xiujianfeng@...wei.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH 3/4] xattr: Use dedicated slab buckets for setxattr()

The setxattr() API can be used for exploiting[1][2][3] use-after-free
type confusion flaws in the kernel. Avoid having a user-controlled size
cache share the global kmalloc allocator by using a separate set of
kmalloc buckets.

Link: https://duasynt.com/blog/linux-kernel-heap-spray [1]
Link: https://etenal.me/archives/1336 [2]
Link: https://github.com/a13xp0p0v/kernel-hack-drill/blob/master/drill_exploit_uaf.c [3]
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: Christian Brauner <brauner@...nel.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...r.kernel.org
---
 fs/xattr.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index 09d927603433..2b06316f1d1f 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -821,6 +821,16 @@ SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
 	return error;
 }
 
+static struct kmem_buckets *xattr_buckets;
+static int __init init_xattr_buckets(void)
+{
+	xattr_buckets = kmem_buckets_create("xattr", 0, 0, 0,
+					    XATTR_LIST_MAX, NULL);
+
+	return 0;
+}
+subsys_initcall(init_xattr_buckets);
+
 /*
  * Extended attribute LIST operations
  */
@@ -833,7 +843,7 @@ listxattr(struct dentry *d, char __user *list, size_t size)
 	if (size) {
 		if (size > XATTR_LIST_MAX)
 			size = XATTR_LIST_MAX;
-		klist = kvmalloc(size, GFP_KERNEL);
+		klist = kmem_buckets_alloc(xattr_buckets, size, GFP_KERNEL);
 		if (!klist)
 			return -ENOMEM;
 	}
-- 
2.34.1