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Message-ID: <20170830112247.GA30640@quack2.suse.cz>
Date: Wed, 30 Aug 2017 13:22:47 +0200
From: Jan Kara <jack@...e.cz>
To: Kees Cook <keescook@...omium.org>
Cc: linux-kernel@...r.kernel.org, David Windsor <dave@...lcore.net>,
Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
linux-mm@...ck.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 08/30] ext2: Define usercopy region in
ext2_inode_cache slab cache
On Mon 28-08-17 14:34:49, Kees Cook wrote:
> From: David Windsor <dave@...lcore.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:
> fs/ext2/super.c:
> ext2_alloc_inode(...):
> struct ext2_inode_info *ei;
> ...
> ei = kmem_cache_alloc(ext2_inode_cachep, GFP_NOFS);
> ...
> return &ei->vfs_inode;
>
> fs/ext2/ext2.h:
> EXT2_I(struct inode *inode):
> return container_of(inode, struct ext2_inode_info, vfs_inode);
>
> fs/ext2/namei.c:
> ext2_symlink(...):
> ...
> inode->i_link = (char *)&EXT2_I(inode)->i_data;
>
> example usage trace:
> readlink_copy+0x43/0x70
> vfs_readlink+0x62/0x110
> SyS_readlinkat+0x100/0x130
>
> fs/namei.c:
> 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
> 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@...lcore.net>
> [kees: adjust commit log, provide usage trace]
> Cc: Jan Kara <jack@...e.com>
> Cc: linux-ext4@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
Looks good. You can add:
Acked-by: Jan Kara <jack@...e.cz>
Honza
> ---
> fs/ext2/super.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 7b1bc9059863..670142cde59d 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -219,11 +219,13 @@ 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|
> - SLAB_MEM_SPREAD|SLAB_ACCOUNT),
> - init_once);
> + ext2_inode_cachep = kmem_cache_create_usercopy("ext2_inode_cache",
> + sizeof(struct ext2_inode_info), 0,
> + (SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD|
> + SLAB_ACCOUNT),
> + 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;
> --
> 2.7.4
>
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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