[PATCH 4.17 06/18] jfs: Fix usercopy whitelist for inline inode data

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@xxxxxxxxxxxx>

commit 961b33c244e5ba1543ae26270a1ba29f29c2db83 upstream.

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 (i_inline_ea) when needed. So the whitelist needed to
be expanded to include both i_inline and 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@xxxxxxxxx>
Fixes: 8d2704d382a9 ("jfs: Define usercopy region in jfs_ip slab cache")
Cc: Dave Kleikamp <shaggy@xxxxxxxxxx>
Cc: jfs-discussion@xxxxxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/jfs/jfs_dinode.h |    7 +++++++
 fs/jfs/jfs_incore.h |    1 +
 fs/jfs/super.c      |    3 +--
 3 files changed, 9 insertions(+), 2 deletions(-)

--- 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];
--- 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
--- 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;