jfs: Fix 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 (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@gmail.com>
Fixes: 8d2704d382a9 ("jfs: Define usercopy region in jfs_ip slab cache")
Cc: Dave Kleikamp <shaggy@kernel.org>
Cc: jfs-discussion@lists.sourceforge.net
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

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;