[11/36] ext2: Define usercopy region in ext2_inode_cache slab cache
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Message ID 1515531365-37423-12-git-send-email-keescook@chromium.org
State New
Headers show

Commit Message

Kees Cook Jan. 9, 2018, 8:55 p.m. UTC
From: David Windsor <dave@nullcore.net>

The ext2 symlink pathnames, stored in struct ext2_inode_info.i_data and
therefore contained in the ext2_inode_cache slab cache, need to be copied
to/from userspace.

cache object allocation:
            struct ext2_inode_info *ei;
            ei = kmem_cache_alloc(ext2_inode_cachep, GFP_NOFS);
            return &ei->vfs_inode;

        EXT2_I(struct inode *inode):
            return container_of(inode, struct ext2_inode_info, vfs_inode);

            inode->i_link = (char *)&EXT2_I(inode)->i_data;

example usage trace:

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

        (inlined into 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
ext2_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 dynamically sized 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 <dave@nullcore.net>
[kees: adjust commit log, provide usage trace]
Cc: Jan Kara <jack@suse.com>
Cc: linux-ext4@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Jan Kara <jack@suse.cz>
 fs/ext2/super.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff mbox

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 7646818ab266..50b8946c3d1a 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -220,11 +220,13 @@  static void init_once(void *foo)
 static int __init init_inodecache(void)
-	ext2_inode_cachep = kmem_cache_create("ext2_inode_cache",
-					     sizeof(struct ext2_inode_info),
-					     0, (SLAB_RECLAIM_ACCOUNT|
-					     init_once);
+	ext2_inode_cachep = kmem_cache_create_usercopy("ext2_inode_cache",
+				sizeof(struct ext2_inode_info), 0,
+				offsetof(struct ext2_inode_info, i_data),
+				sizeof_field(struct ext2_inode_info, i_data),
+				init_once);
 	if (ext2_inode_cachep == NULL)
 		return -ENOMEM;
 	return 0;