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Date: Tue,  9 Jan 2018 12:55:41 -0800
From: Kees Cook <>
Cc: Kees Cook <>,
	David Windsor <>,
	Dave Kleikamp <>,,
	Linus Torvalds <>,
	Alexander Viro <>,
	Andrew Morton <>,
	Andy Lutomirski <>,
	Christoph Hellwig <>,
	Christoph Lameter <>,
	"David S. Miller" <>,
	Laura Abbott <>,
	Mark Rutland <>,
	"Martin K. Petersen" <>,
	Paolo Bonzini <>,
	Christian Borntraeger <>,
	Christoffer Dall <>,
	Dave Kleikamp <>,
	Jan Kara <>,
	Luis de Bethencourt <>,
	Marc Zyngier <>,
	Rik van Riel <>,
	Matthew Garrett <>,,,,,
Subject: [PATCH 12/36] jfs: Define usercopy region in jfs_ip slab cache

From: David Windsor <>

The jfs symlink pathnames, stored in struct jfs_inode_info.i_inline and
therefore contained in the jfs_ip slab cache, need to be copied to/from

cache object allocation:
            jfs_inode = kmem_cache_alloc(jfs_inode_cachep, GFP_NOFS);
            return &jfs_inode->vfs_inode;

        JFS_IP(struct inode *inode):
            return container_of(inode, struct jfs_inode_info, vfs_inode);

            inode->i_link = JFS_IP(inode)->i_inline;

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
jfs_ip 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 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 <>
[kees: adjust commit log, provide usage trace]
Cc: Dave Kleikamp <>
Signed-off-by: Kees Cook <>
Acked-by: Dave Kleikamp <>
 fs/jfs/super.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/jfs/super.c b/fs/jfs/super.c
index 90373aebfdca..1b9264fd54b6 100644
--- a/fs/jfs/super.c
+++ b/fs/jfs/super.c
@@ -965,9 +965,11 @@ static int __init init_jfs_fs(void)
 	int rc;
 	jfs_inode_cachep =
-	    kmem_cache_create("jfs_ip", sizeof(struct jfs_inode_info), 0,
-			    init_once);
+	    kmem_cache_create_usercopy("jfs_ip", sizeof(struct jfs_inode_info),
+			offsetof(struct jfs_inode_info, i_inline),
+			sizeof_field(struct jfs_inode_info, i_inline),
+			init_once);
 	if (jfs_inode_cachep == NULL)
 		return -ENOMEM;

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