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[PATCH 07/23] exofs: define usercopy region in exofs_inode_cache slab cache

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  [PATCH 07/23] exofs: define usercopy region in exofs_inode_cache slab cache Kees Cook <keescook@chromium.org> - 2017-06-20 01:40 +0200

#1670029 — [PATCH 07/23] exofs: define usercopy region in exofs_inode_cache slab cache

From: David Windsor <dave@nullcore.net>

exofs short symlink names and device #'s, stored in struct
exofs_i_info.i_data and therefore contained in the exofs_inode_cache
slab cache, need to be copied to/from userspace.

In support of usercopy hardening, this patch defines a region in
the exofs_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@nullcore.net>
[kees: adjust commit log]
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 fs/exofs/super.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/exofs/super.c b/fs/exofs/super.c
index 819624cfc8da..e5c532875bb7 100644
--- a/fs/exofs/super.c
+++ b/fs/exofs/super.c
@@ -192,10 +192,13 @@ static void exofs_init_once(void *foo)
  */
 static int init_inodecache(void)
 {
-	exofs_inode_cachep = kmem_cache_create("exofs_inode_cache",
+	exofs_inode_cachep = kmem_cache_create_usercopy("exofs_inode_cache",
 				sizeof(struct exofs_i_info), 0,
 				SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD |
-				SLAB_ACCOUNT, exofs_init_once);
+				SLAB_ACCOUNT,
+				offsetof(struct exofs_i_info, i_data),
+				sizeof_field(struct exofs_i_info, i_data),
+				exofs_init_once);
 	if (exofs_inode_cachep == NULL)
 		return -ENOMEM;
 	return 0;
-- 
2.7.4

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