This is a note to let you know that I've just added the patch titled ntfs: fix use-after-free in ntfs_attr_find() to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ntfs-fix-use-after-free-in-ntfs_attr_find.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From d85a1bec8e8d552ab13163ca1874dcd82f3d1550 Mon Sep 17 00:00:00 2001 From: Hawkins Jiawei <yin31149@xxxxxxxxx> Date: Thu, 1 Sep 2022 00:09:34 +0800 Subject: ntfs: fix use-after-free in ntfs_attr_find() From: Hawkins Jiawei <yin31149@xxxxxxxxx> commit d85a1bec8e8d552ab13163ca1874dcd82f3d1550 upstream. Patch series "ntfs: fix bugs about Attribute", v2. 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, the kernel triggersa KASAN use-after-free detection as reported by Syzkaller. Although one of patch 1 or patch 2 can fix this, 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. This patch (of 3): 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. Link: https://lkml.kernel.org/r/20220831160935.3409-1-yin31149@xxxxxxxxx Link: https://lkml.kernel.org/r/20220831160935.3409-2-yin31149@xxxxxxxxx Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx> Cc: Anton Altaparmakov <anton@xxxxxxxxxx> Cc: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx> Cc: syzkaller-bugs <syzkaller-bugs@xxxxxxxxxxxxxxxx> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/ntfs/inode.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/fs/ntfs/inode.c +++ b/fs/ntfs/inode.c @@ -1863,6 +1863,13 @@ int ntfs_read_inode_mount(struct inode * 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); Patches currently in stable-queue which might be from yin31149@xxxxxxxxx are queue-4.9/ntfs-check-overflow-when-iterating-attr_records.patch queue-4.9/ntfs-fix-out-of-bounds-read-in-ntfs_attr_find.patch queue-4.9/ntfs-fix-use-after-free-in-ntfs_attr_find.patch