[PATCH v2 0/3] ntfs: fix bugs about Attribute

[PATCH v2 0/3] ntfs: fix bugs about Attribute

[Hawkins Jiawei]

This patchset fixes three bugs relative to Attribute in record:

Patch 1 adds a sanity check to ensure that, attrs_offset field in
first mft record loading from disk is within bounds.

Patch 2 moves the ATTR_RECORD's bounds checking earlier, to avoid
dereferencing ATTR_RECORD before checking this ATTR_RECORD is within
bounds.

Patch 3 adds an overflow checking to avoid possible forever loop in
ntfs_attr_find().

Without patch 1 and patch 2, kernel may trigger following problem
reported by Syzkaller:
==================================================================
BUG: KASAN: use-after-free in ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
Read of size 2 at addr ffff88807e352009 by task syz-executor153/3607

[...]
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:317 [inline]
 print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
 ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
 ntfs_attr_lookup+0x1056/0x2070 fs/ntfs/attrib.c:1193
 ntfs_read_inode_mount+0x89a/0x2580 fs/ntfs/inode.c:1845
 ntfs_fill_super+0x1799/0x9320 fs/ntfs/super.c:2854
 mount_bdev+0x34d/0x410 fs/super.c:1400
 legacy_get_tree+0x105/0x220 fs/fs_context.c:610
 vfs_get_tree+0x89/0x2f0 fs/super.c:1530
 do_new_mount fs/namespace.c:3040 [inline]
 path_mount+0x1326/0x1e20 fs/namespace.c:3370
 do_mount fs/namespace.c:3383 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount fs/namespace.c:3568 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 [...]
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0001f8d400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7e350
head:ffffea0001f8d400 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888011842140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
 ffff88807e351f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807e351f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807e352000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88807e352080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807e352100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Although one of patch 1 or patch 2 can fix above bug,  we still
need both of them. Because patch 1 fixes the root cause, and
patch 2 not only fixes the direct cause, but also fixes the
potential out-of-bounds bug.

v1->v2:
 * Refactor check on Attribute Record Header
suggested by Dan Carpenter.
 * Add check bounds on ATTR_RECORD's length suggested
by Dan Carpenter.

Hawkins Jiawei (3):
  ntfs: fix use-after-free in ntfs_attr_find()
  ntfs: fix out-of-bounds read in ntfs_attr_find()
  ntfs: check overflow when iterates ATTR_RECORDs

 fs/ntfs/attrib.c | 28 ++++++++++++++++++++++++----
 fs/ntfs/inode.c  |  7 +++++++
 2 files changed, 31 insertions(+), 4 deletions(-)

-- 
2.25.1

[PATCH v2 1/3] ntfs: fix use-after-free in ntfs_attr_find()

[Hawkins Jiawei]

Syzkaller reported use-after-free read as follows:
==================================================================
BUG: KASAN: use-after-free in ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
Read of size 2 at addr ffff88807e352009 by task syz-executor153/3607

[...]
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:317 [inline]
 print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
 ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
 ntfs_attr_lookup+0x1056/0x2070 fs/ntfs/attrib.c:1193
 ntfs_read_inode_mount+0x89a/0x2580 fs/ntfs/inode.c:1845
 ntfs_fill_super+0x1799/0x9320 fs/ntfs/super.c:2854
 mount_bdev+0x34d/0x410 fs/super.c:1400
 legacy_get_tree+0x105/0x220 fs/fs_context.c:610
 vfs_get_tree+0x89/0x2f0 fs/super.c:1530
 do_new_mount fs/namespace.c:3040 [inline]
 path_mount+0x1326/0x1e20 fs/namespace.c:3370
 do_mount fs/namespace.c:3383 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount fs/namespace.c:3568 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 [...]
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0001f8d400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7e350
head:ffffea0001f8d400 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888011842140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
 ffff88807e351f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807e351f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807e352000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88807e352080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807e352100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Kernel will loads $MFT/$DATA's first mft record in
ntfs_read_inode_mount().

Yet the problem is that after loading, kernel doesn't check whether
attrs_offset field is a valid value.

To be more specific, if attrs_offset field is larger
than bytes_allocated field, then it may trigger the out-of-bounds read
bug(reported as use-after-free bug) in ntfs_attr_find(), when kernel
tries to access the corresponding mft record's attribute.

This patch solves it by adding the sanity check between attrs_offset
field and bytes_allocated field, after loading the first mft record.

Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
v1->v2:
 * No change.

 fs/ntfs/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index db0f1995aedd..08c659332e26 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -1829,6 +1829,13 @@ int ntfs_read_inode_mount(struct inode *vi)
 		goto err_out;
 	}
 
+	/* Sanity check offset to the first attribute */
+	if (le16_to_cpu(m->attrs_offset) >= le32_to_cpu(m->bytes_allocated)) {
+		ntfs_error(sb, "Incorrect mft offset to the first attribute %u in superblock.",
+			       le16_to_cpu(m->attrs_offset));
+		goto err_out;
+	}
+
 	/* Need this to sanity check attribute list references to $MFT. */
 	vi->i_generation = ni->seq_no = le16_to_cpu(m->sequence_number);
 
-- 
2.25.1

[PATCH v2 2/3] ntfs: fix out-of-bounds read in ntfs_attr_find()

[Hawkins Jiawei]

Kernel will iterates over ATTR_RECORDs in mft record in ntfs_attr_find().
To ensure access on these ATTR_RECORDs are within bounds, kernel will
do some checking during iteration.

The problem is that during checking whether ATTR_RECORD's name is within
bounds, kernel will dereferences the ATTR_RECORD name_offset field,
before checking this ATTR_RECORD strcture is within bounds. This problem
may result out-of-bounds read in ntfs_attr_find(), reported by
Syzkaller:

==================================================================
BUG: KASAN: use-after-free in ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
Read of size 2 at addr ffff88807e352009 by task syz-executor153/3607

[...]
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:317 [inline]
 print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
 ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
 ntfs_attr_lookup+0x1056/0x2070 fs/ntfs/attrib.c:1193
 ntfs_read_inode_mount+0x89a/0x2580 fs/ntfs/inode.c:1845
 ntfs_fill_super+0x1799/0x9320 fs/ntfs/super.c:2854
 mount_bdev+0x34d/0x410 fs/super.c:1400
 legacy_get_tree+0x105/0x220 fs/fs_context.c:610
 vfs_get_tree+0x89/0x2f0 fs/super.c:1530
 do_new_mount fs/namespace.c:3040 [inline]
 path_mount+0x1326/0x1e20 fs/namespace.c:3370
 do_mount fs/namespace.c:3383 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount fs/namespace.c:3568 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 [...]
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0001f8d400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7e350
head:ffffea0001f8d400 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888011842140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
 ffff88807e351f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807e351f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807e352000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88807e352080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807e352100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

This patch solves it by moving the ATTR_RECORD strcture's bounds
checking earlier, then checking whether ATTR_RECORD's name
is within bounds. What's more, this patch also add some comments
to improve its maintainability.

Reported-and-tested-by: syzbot+5f8dcabe4a3b2c51c607@syzkaller.appspotmail.com
Signed-off-by: chenxiaosong (A) <chenxiaosong2@huawei.com>
Link: https://lore.kernel.org/all/1636796c-c85e-7f47-e96f-e074fee3c7d3@huawei.com/
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://groups.google.com/g/syzkaller-bugs/c/t_XdeKPGTR4/m/LECAuIGcBgAJ
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
v1->v2:
 * Refactor check on Attribute Record Header
suggested by Dan Carpenter.

 fs/ntfs/attrib.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index 52615e6090e1..cec4be2a2d23 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -594,11 +594,23 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
 	for (;;	a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
 		u8 *mrec_end = (u8 *)ctx->mrec +
 		               le32_to_cpu(ctx->mrec->bytes_allocated);
-		u8 *name_end = (u8 *)a + le16_to_cpu(a->name_offset) +
-			       a->name_length * sizeof(ntfschar);
-		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end ||
-		    name_end > mrec_end)
+		u8 *name_end;
+
+		/* check whether ATTR_RECORD wrap */
+		if ((u8 *)a < (u8 *)ctx->mrec)
+			break;
+
+		/* check whether Attribute Record Header is within bounds */
+		if ((u8 *)a > mrec_end ||
+		    (u8 *)a + sizeof(ATTR_RECORD) > mrec_end)
 			break;
+
+		/* check whether ATTR_RECORD's name is within bounds */
+		name_end = (u8 *)a + le16_to_cpu(a->name_offset) +
+			   a->name_length * sizeof(ntfschar);
+		if (name_end > mrec_end)
+			break;
+
 		ctx->attr = a;
 		if (unlikely(le32_to_cpu(a->type) > le32_to_cpu(type) ||
 				a->type == AT_END))
-- 
2.25.1

[PATCH v2 3/3] ntfs: check overflow when iterates ATTR_RECORDs

[Hawkins Jiawei]

Kernel will iterates over ATTR_RECORDs in mft record in ntfs_attr_find().
Because the ATTR_RECORDs are next to each other, kernel can get the next
ATTR_RECORD from end address of current ATTR_RECORD, through current
ATTR_RECORD length field.

The problem is that during iteration, when kernel calculates the end address
of current ATTR_RECORD, kernel may trigger an integer overflow bug in
executing `a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))`. This
may wrap, leading to a forever iteration on 32bit systems.

This patch solves it by adding some checks on calculating end address
of current ATTR_RECORD during iteration.

Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/all/20220827105842.GM2030@kadam/
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
v1->v2:
 * Add check bounds on ATTR_RECORD's length suggested
by Dan Carpenter.

 fs/ntfs/attrib.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index cec4be2a2d23..a3865bc4a0c6 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -617,6 +617,14 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
 			return -ENOENT;
 		if (unlikely(!a->length))
 			break;
+
+		/* check whether ATTR_RECORD's length wrap */
+		if ((u8 *)a + le32_to_cpu(a->length) < (u8 *)a)
+			break;
+		/* check whether ATTR_RECORD's length is within bounds */
+		if ((u8 *)a + le32_to_cpu(a->length) > mrec_end)
+			break;
+
 		if (a->type != type)
 			continue;
 		/*
-- 
2.25.1