From 80344266c19b82a27e018083e9dd501048a6a06a Mon Sep 17 00:00:00 2001 From: David Windsor Date: Sat, 10 Jun 2017 22:50:44 -0400 Subject: [PATCH] dcache: Define usercopy region in dentry_cache slab cache 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 [kees: adjust hunks for kmalloc-specific things moved later] [kees: adjust commit log, provide usage trace] Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Kees Cook --- fs/dcache.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 5c7df1df81ff..92ad7a2168e1 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -3601,8 +3601,9 @@ static void __init dcache_init(void) * but it is probably not worth it because of the cache nature * of the dcache. */ - dentry_cache = KMEM_CACHE(dentry, - SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT); + dentry_cache = KMEM_CACHE_USERCOPY(dentry, + SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT, + d_iname); /* Hash may have been set up in dcache_init_early */ if (!hashdist)