Bug 199347

Summary: buffer overflow in ext4_xattr_set_entry() when mounting and operating a crafted ext4 image
Product: File System Reporter: Wen Xu (wen.xu)
Component: ext4Assignee: fs_ext4 (fs_ext4)
Status: RESOLVED CODE_FIX    
Severity: normal CC: carnil, MohammadRasoulFarajollahi, tytso, wen.xu
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 4.15, 4.16, 4.17 Subsystem:
Regression: No Bisected commit-id:
Attachments: The crafted image which causes overflow
poc.c
ext4: correctly handle a zero-length xattr with a non-zero e_value_offs

Description Wen Xu 2018-04-11 03:01:15 UTC 
Created attachment 275283 [details]
The crafted image which causes overflow

- Overview
Buffer overflow in ext4_xattr_set_entry() when mounting and operating a crafted ext4 image

- Reproduce (Tested on 4.16.0-rc1, latest ext4 dev branch)
# mkdir mnt
# mount -t ext4 2.img mnt
# gcc -o poc poc.c
# ./poc ./mnt

- Reason
https://elixir.bootlin.com/linux/v4.15/source/fs/ext4/xattr.c#L1671
`
		void *first_val = s->base + min_offs;
		size_t offs = le16_to_cpu(here->e_value_offs);
		void *val = s->base + offs;

		memmove(first_val + old_size, first_val, val - first_val);
		memset(first_val, 0, old_size);
		min_offs += old_size;
`
kernel misses check on val, where val - first_val can become negative, which leads to heap overflow

- Kernel dump
[   41.225365] EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null)
[   44.538641] BUG: unable to handle kernel paging request at ffff9ec9a3000000
[   44.538733] IP: __memmove+0x81/0x1a0
[   44.538755] PGD 1249bd067 P4D 1249bd067 PUD 1249c1067 PMD 80000001230000e1
[   44.538793] Oops: 0003 [#1] SMP PTI
[   44.538815] Modules linked in: snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core snd_pcm snd_timer snd soundcore i2c_piix4 mac_hid ib_iser rdma_cm iw_cm ib_cm ib_core iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi autofs4 btrfs zstd_decompress zstd_compress xxhash raid10 raid456 libcrc32c async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq raid1 raid0 multipath linear qxl 8139too drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm crct10dif_pclmul drm 8139cp floppy crc32_pclmul aesni_intel aes_x86_64 crypto_simd cryptd pata_acpi glue_helper mii
[   44.539074] CPU: 0 PID: 1470 Comm: poc Not tainted 4.16.0-rc1+ #1
[   44.539104] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[   44.539147] RIP: 0010:__memmove+0x81/0x1a0
[   44.539170] RSP: 0018:ffffb84e00cb7a30 EFLAGS: 00010203
[   44.539199] RAX: ffff9ec9a15a6400 RBX: ffffb84e00cb7c38 RCX: 1fffffffffcb4c7e
[   44.539231] RDX: fffffffffffffff4 RSI: ffff9ec9a3000000 RDI: ffff9ec9a3000000
[   44.539263] RBP: ffffb84e00cb7bb0 R08: 0000000000000000 R09: ffffffff83321992
[   44.539295] R10: ffff9ec9a15a63ec R11: 0000000000000000 R12: ffff9ec9a15a6020
[   44.539328] R13: 00000000000003f4 R14: ffff9ec9a15a6400 R15: 0000000000000000
[   44.539361] FS:  00007f3628101700(0000) GS:ffff9ec9bfc00000(0000) knlGS:0000000000000000
[   44.539397] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   44.539424] CR2: ffff9ec9a3000000 CR3: 0000000138c52000 CR4: 00000000000006f0
[   44.539475] Call Trace:
[   44.539832]  ext4_xattr_set_entry+0x9e7/0xf80
[   44.539871]  ? jbd2_journal_cancel_revoke+0xbb/0xe0
[   44.539897]  ? do_get_write_access+0x318/0x400
[   44.539924]  ? kmem_cache_alloc+0xd9/0x1b0
[   44.539946]  ? jbd2_journal_get_write_access+0x54/0x60
[   44.539972]  ext4_xattr_block_set+0x212/0xea0
[   44.539998]  ? _cond_resched+0x16/0x40
[   44.540019]  ? xattr_find_entry+0x89/0x110
[   44.540041]  ext4_xattr_set_handle+0x514/0x610
[   44.540065]  ext4_xattr_set+0x7f/0x120
[   44.540090]  __vfs_removexattr+0x4d/0x60
[   44.540112]  vfs_removexattr+0x75/0xe0
[   44.540132]  removexattr+0x4d/0x80
[   44.540152]  ? kmem_cache_alloc+0xd9/0x1b0
[   44.540174]  ? _cond_resched+0x16/0x40
[   44.540194]  ? kmem_cache_alloc+0xd9/0x1b0
[   44.540217]  ? _cond_resched+0x16/0x40
[   44.540238]  ? __mnt_want_write+0x54/0x60
[   44.540259]  ? mnt_want_write+0x28/0x50
[   44.540279]  path_removexattr+0x91/0xb0
[   44.540300]  SyS_removexattr+0xf/0x20
[   44.540322]  do_syscall_64+0x71/0x120
[   44.540344]  entry_SYSCALL_64_after_hwframe+0x21/0x86
[   44.541387] RIP: 0033:0x7f3627c221c7
[   44.542304] RSP: 002b:00007ffe569d7248 EFLAGS: 00000206 ORIG_RAX: 00000000000000c5
[   44.543244] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3627c221c7
[   44.544186] RDX: 0000000000000071 RSI: 0000000000401489 RDI: 000000000233f0c0
[   44.545111] RBP: 00007ffe569d73b0 R08: 000000000233f0a0 R09: 0000000000000000
[   44.546025] R10: 0000000000000595 R11: 0000000000000206 R12: 0000000000400c20
[   44.546935] R13: 00007ffe569d74b0 R14: 0000000000000000 R15: 0000000000000000
[   44.547829] Code: 08 4c 89 4f 10 4c 89 47 18 48 8d 7f 20 73 d4 48 83 c2 20 e9 a2 00 00 00 66 90 48 89 d1 4c 8b 5c 16 f8 4c 8d 54 17 f8 48 c1 e9 03 <f3> 48 a5 4d 89 1a e9 0c 01 00 00 0f 1f 40 00 48 89 d1 4c 8b 1e
[   44.549629] RIP: __memmove+0x81/0x1a0 RSP: ffffb84e00cb7a30
[   44.550479] CR2: ffff9ec9a3000000
[   44.551304] ---[ end trace 71ac2ebfa045556f ]---
Comment 1 Wen Xu 2018-04-11 03:01:37 UTC 
Created attachment 275285 [details]
poc.c
Comment 2 Wen Xu 2018-04-11 03:01:58 UTC 
Reported by Wen Xu from SSLab, Gatech.
Comment 3 Wen Xu 2018-04-23 17:52:07 UTC 
The issue still exists in 4.17-rc2 so far.
Comment 4 Theodore Tso 2018-05-23 17:02:05 UTC 
Created attachment 276147 [details]
ext4: correctly handle a zero-length xattr with a  non-zero e_value_offs

This patch should address the problem.
Comment 5 Theodore Tso 2018-05-25 01:02:43 UTC 
A CVE number has been assigned for this: CVE-2018-10840
Comment 6 Wen Xu 2018-05-25 01:21:02 UTC 
Many thanks for your response, Ted!
Comment 7 MohammadRasoulFarajollahi 2018-07-25 08:48:42 UTC 
Comment on attachment 275283 [details]
The crafted image which causes overflow

file:///home/mrfarajollahi/Downloads/2(1).img