linux-kernel - [PATCH] jfs: Expand usercopy whitelist for inline inode data

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Date:   Fri, 3 Aug 2018 13:05:51 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Bart Massey <bart.massey@...il.com>,
        Dave Kleikamp <shaggy@...nel.org>,
        jfs-discussion@...ts.sourceforge.net,
        David Windsor <dave@...lcore.net>
Subject: [PATCH] jfs: Expand usercopy whitelist for inline inode data

Bart Massey reported what turned out to be a usercopy whitelist false
positive in JFS when symlink contents exceeded 128 bytes. The inline
inode data (i_inline) is actually designed to overflow into the "extended
area" following it when needed. So the whitelist needed to be expanded
to include i_inline_ea (the whole size of which is calculated internally
using IDATASIZE, 256, instead of sizeof(i_inline), 128).

$ cd /mnt/jfs
$ touch $(perl -e 'print "B" x 250')
$ ln -s B* b
$ ls -l >/dev/null

[  249.436410] Bad or missing usercopy whitelist? Kernel memory exposure attempt detected from SLUB object 'jfs_ip' (offset 616, size 250)!

Reported-by: Bart Massey <bart.massey@...il.com>
Fixes: 8d2704d382a9 ("jfs: Define usercopy region in jfs_ip slab cache")
Cc: stable@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
I intend this to land via the usercopy tree...
---
 fs/jfs/jfs_dinode.h | 7 +++++++
 fs/jfs/jfs_incore.h | 1 +
 fs/jfs/super.c      | 3 +--
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/jfs/jfs_dinode.h b/fs/jfs/jfs_dinode.h
index 395c4c0d0f06..1682a87c00b2 100644
--- a/fs/jfs/jfs_dinode.h
+++ b/fs/jfs/jfs_dinode.h
@@ -115,6 +115,13 @@ struct dinode {
 					dxd_t _dxd;	/* 16: */
 					union {
 						__le32 _rdev;	/* 4: */
+						/*
+						 * The fast symlink area
+						 * is expected to overflow
+						 * into _inlineea when
+						 * needed (which will clear
+						 * INLINEEA).
+						 */
 						u8 _fastsymlink[128];
 					} _u;
 					u8 _inlineea[128];
diff --git a/fs/jfs/jfs_incore.h b/fs/jfs/jfs_incore.h
index 1f26d1910409..9940a1e04cbf 100644
--- a/fs/jfs/jfs_incore.h
+++ b/fs/jfs/jfs_incore.h
@@ -87,6 +87,7 @@ struct jfs_inode_info {
 		struct {
 			unchar _unused[16];	/* 16: */
 			dxd_t _dxd;		/* 16: */
+			/* _inline may overflow into _inline_ea when needed */
 			unchar _inline[128];	/* 128: inline symlink */
 			/* _inline_ea may overlay the last part of
 			 * file._xtroot if maxentry = XTROOTINITSLOT
diff --git a/fs/jfs/super.c b/fs/jfs/super.c
index 1b9264fd54b6..f08571433aba 100644
--- a/fs/jfs/super.c
+++ b/fs/jfs/super.c
@@ -967,8 +967,7 @@ static int __init init_jfs_fs(void)
 	jfs_inode_cachep =
 	    kmem_cache_create_usercopy("jfs_ip", sizeof(struct jfs_inode_info),
 			0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
-			offsetof(struct jfs_inode_info, i_inline),
-			sizeof_field(struct jfs_inode_info, i_inline),
+			offsetof(struct jfs_inode_info, i_inline), IDATASIZE,
 			init_once);
 	if (jfs_inode_cachep == NULL)
 		return -ENOMEM;
-- 
2.17.1


-- 
Kees Cook
Pixel Security