• David Windsor's avatar
    befs: Define usercopy region in befs_inode_cache slab cache · 0fc256d3
    David Windsor authored
    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:
        fs/befs/linuxvfs.c:
            befs_alloc_inode(...):
                ...
                bi = kmem_cache_alloc(befs_inode_cachep, GFP_KERNEL);
                ...
                return &bi->vfs_inode;
    
            befs_iget(...):
                ...
                strlcpy(befs_ino->i_data.symlink, raw_inode->data.symlink,
                        BEFS_SYMLINK_LEN);
                ...
                inode->i_link = befs_ino->i_data.symlink;
    
    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 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
    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: 's avatarDavid Windsor <dave@nullcore.net>
    [kees: adjust commit log, provide usage trace]
    Cc: Luis de Bethencourt <luisbg@kernel.org>
    Cc: Salah Triki <salah.triki@gmail.com>
    Signed-off-by: 's avatarKees Cook <keescook@chromium.org>
    Acked-by: 's avatarLuis de Bethencourt <luisbg@kernel.org>
    0fc256d3
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