[PATCH 09/23] ext4: define usercopy region in ext4_inode_cache slab cache

[Kees Cook]

From: David Windsor <dave@xxxxxxxxxxxx>

The ext4 symlink pathnames, stored in struct ext4_inode_info.i_data
and therefore contained in the ext4_inode_cache slab cache, need
to be copied to/from userspace.

In support of usercopy hardening, this patch defines a region in
the ext4_inode_cache slab cache in which userspace copy operations
are allowed.

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 <dave@xxxxxxxxxxxx>
[kees: adjust commit log]
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/ext4/super.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d37c81f327e7..bd92123cf1fc 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1031,11 +1031,13 @@ static void init_once(void *foo)
 
 static int __init init_inodecache(void)
 {
-	ext4_inode_cachep = kmem_cache_create("ext4_inode_cache",
-					     sizeof(struct ext4_inode_info),
-					     0, (SLAB_RECLAIM_ACCOUNT|
-						SLAB_MEM_SPREAD|SLAB_ACCOUNT),
-					     init_once);
+	ext4_inode_cachep = kmem_cache_create_usercopy("ext4_inode_cache",
+				sizeof(struct ext4_inode_info), 0,
+				(SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD|
+					SLAB_ACCOUNT),
+				offsetof(struct ext4_inode_info, i_data),
+				sizeof_field(struct ext4_inode_info, i_data),
+				init_once);
 	if (ext4_inode_cachep == NULL)
 		return -ENOMEM;
 	return 0;
-- 
2.7.4