Ext4 will always create ext4 extended attributes which do not have a value (where e_value_size is zero) with e_value_offs set to zero. In most places e_value_offs will not be used in a substantive way if e_value_size is zero. There was one exception to this, which is in ext4_xattr_set_entry(), where if there is a maliciously crafted file system where there is an extended attribute with e_value_offs is non-zero and e_values_size is 0, the attempt to remove this xattr will result in a negative value getting passed to memmove, leading to the following sadness: [ 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 ]--- https://bugzilla.kernel.org/show_bug.cgi?id=199347 Reported-by: "Xu, Wen" <wen.xu@xxxxxxxxxx> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Cc: stable@xxxxxxxxxx Fixes: dec214d00e0d7 ("ext4: xattr inode deduplication") --- fs/ext4/xattr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 499cb4b1fbd2..fc4ced59c565 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1688,7 +1688,7 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i, /* No failures allowed past this point. */ - if (!s->not_found && here->e_value_offs) { + if (!s->not_found && here->e_value_size && here->e_value_offs) { /* Remove the old value. */ void *first_val = s->base + min_offs; size_t offs = le16_to_cpu(here->e_value_offs); -- 2.16.1.72.g5be1f00a9a
