Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 28 Aug 2017 14:34:51 -0700
From: Kees Cook <>
Cc: Kees Cook <>,
	David Windsor <>,
	Luis de Bethencourt <>,
	Salah Triki <>,,
Subject: [PATCH v2 10/30] befs: Define usercopy region in befs_inode_cache slab cache

From: David Windsor <>

befs symlink pathnames, stored in struct befs_inode_info.i_data.symlink
and therefore contained in the befs_inode_cache slab cache, need to be
copied to/from userspace.

cache object allocation:
            bi = kmem_cache_alloc(befs_inode_cachep, GFP_KERNEL);
            return &bi->vfs_inode;

            strlcpy(befs_ino->i_data.symlink, raw_inode->data.symlink,
            inode->i_link = befs_ino->i_data.symlink;

example usage trace:

        readlink_copy(..., link):
            copy_to_user(..., link, len);

        (inlined in vfs_readlink)
        generic_readlink(dentry, ...):
            struct inode *inode = d_inode(dentry);
            const char *link = inode->i_link;
            readlink_copy(..., link);

In support of usercopy hardening, this patch defines a region in the
befs_inode_cache slab cache in which userspace copy operations are

This region is known as the slab cache's usercopy region. Slab caches can
now check that each copy operation involving cache-managed memory falls
entirely within the slab's usercopy region.

This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY
whitelisting code in the last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code are
mine and don't reflect the original grsecurity/PaX code.

Signed-off-by: David Windsor <>
[kees: adjust commit log, provide usage trace]
Cc: Luis de Bethencourt <>
Cc: Salah Triki <>
Signed-off-by: Kees Cook <>
 fs/befs/linuxvfs.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/befs/linuxvfs.c b/fs/befs/linuxvfs.c
index 4a4a5a366158..1c2dcbee79dd 100644
--- a/fs/befs/linuxvfs.c
+++ b/fs/befs/linuxvfs.c
@@ -444,11 +444,15 @@ static struct inode *befs_iget(struct super_block *sb, unsigned long ino)
 static int __init
-	befs_inode_cachep = kmem_cache_create("befs_inode_cache",
-					      sizeof (struct befs_inode_info),
-					      0, (SLAB_RECLAIM_ACCOUNT|
-					      init_once);
+	befs_inode_cachep = kmem_cache_create_usercopy("befs_inode_cache",
+				sizeof(struct befs_inode_info), 0,
+				offsetof(struct befs_inode_info,
+					i_data.symlink),
+				sizeof_field(struct befs_inode_info,
+					i_data.symlink),
+				init_once);
 	if (befs_inode_cachep == NULL)
 		return -ENOMEM;

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.