80344266c1
When a dentry name is short enough, it can be stored directly in the
dentry itself (instead in a separate kmalloc allocation). These dentry
short names, stored in struct dentry.d_iname and therefore contained in
the dentry_cache slab cache, need to be coped to userspace.
cache object allocation:
fs/dcache.c:
__d_alloc(...):
...
dentry = kmem_cache_alloc(dentry_cache, ...);
...
dentry->d_name.name = dentry->d_iname;
example usage trace:
filldir+0xb0/0x140
dcache_readdir+0x82/0x170
iterate_dir+0x142/0x1b0
SyS_getdents+0xb5/0x160
fs/readdir.c:
(called via ctx.actor by dir_emit)
filldir(..., const char *name, ...):
...
copy_to_user(..., name, namlen)
fs/libfs.c:
dcache_readdir(...):
...
next = next_positive(dentry, p, 1)
...
dir_emit(..., next->d_name.name, ...)
In support of usercopy hardening, this patch defines a region in the
dentry_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 dynamic 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 hunks for kmalloc-specific things moved later]
[kees: adjust commit log, provide usage trace]
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.