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

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