Re: [PATCH v4] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0

From: "Theodore Ts'o" <tytso@mit.edu>
To: adilger.kernel@dilger.ca, lhenriques@suse.de
Cc: "Theodore Ts'o" <tytso@mit.edu>,
	libaokun1@huawei.com, wenqingliu0120@gmail.com,
	linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0
Date: Thu, 22 Sep 2022 10:52:27 -0400	[thread overview]
Message-ID: <166385832826.2997827.14384118128769939622.b4-ty@mit.edu> (raw)
In-Reply-To: <20220822094235.2690-1-lhenriques@suse.de>

On Mon, 22 Aug 2022 10:42:35 +0100, Luís Henriques wrote:
> When walking through an inode extents, the ext4_ext_binsearch_idx() function
> assumes that the extent header has been previously validated.  However, there
> are no checks that verify that the number of entries (eh->eh_entries) is
> non-zero when depth is > 0.  And this will lead to problems because the
> EXT_FIRST_INDEX() and EXT_LAST_INDEX() will return garbage and result in this:
> 
> [  135.245946] ------------[ cut here ]------------
> [  135.247579] kernel BUG at fs/ext4/extents.c:2258!
> [  135.249045] invalid opcode: 0000 [#1] PREEMPT SMP
> [  135.250320] CPU: 2 PID: 238 Comm: tmp118 Not tainted 5.19.0-rc8+ #4
> [  135.252067] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
> [  135.255065] RIP: 0010:ext4_ext_map_blocks+0xc20/0xcb0
> [  135.256475] Code:
> [  135.261433] RSP: 0018:ffffc900005939f8 EFLAGS: 00010246
> [  135.262847] RAX: 0000000000000024 RBX: ffffc90000593b70 RCX: 0000000000000023
> [  135.264765] RDX: ffff8880038e5f10 RSI: 0000000000000003 RDI: ffff8880046e922c
> [  135.266670] RBP: ffff8880046e9348 R08: 0000000000000001 R09: ffff888002ca580c
> [  135.268576] R10: 0000000000002602 R11: 0000000000000000 R12: 0000000000000024
> [  135.270477] R13: 0000000000000000 R14: 0000000000000024 R15: 0000000000000000
> [  135.272394] FS:  00007fdabdc56740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000
> [  135.274510] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  135.276075] CR2: 00007ffc26bd4f00 CR3: 0000000006261004 CR4: 0000000000170ea0
> [  135.277952] Call Trace:
> [  135.278635]  <TASK>
> [  135.279247]  ? preempt_count_add+0x6d/0xa0
> [  135.280358]  ? percpu_counter_add_batch+0x55/0xb0
> [  135.281612]  ? _raw_read_unlock+0x18/0x30
> [  135.282704]  ext4_map_blocks+0x294/0x5a0
> [  135.283745]  ? xa_load+0x6f/0xa0
> [  135.284562]  ext4_mpage_readpages+0x3d6/0x770
> [  135.285646]  read_pages+0x67/0x1d0
> [  135.286492]  ? folio_add_lru+0x51/0x80
> [  135.287441]  page_cache_ra_unbounded+0x124/0x170
> [  135.288510]  filemap_get_pages+0x23d/0x5a0
> [  135.289457]  ? path_openat+0xa72/0xdd0
> [  135.290332]  filemap_read+0xbf/0x300
> [  135.291158]  ? _raw_spin_lock_irqsave+0x17/0x40
> [  135.292192]  new_sync_read+0x103/0x170
> [  135.293014]  vfs_read+0x15d/0x180
> [  135.293745]  ksys_read+0xa1/0xe0
> [  135.294461]  do_syscall_64+0x3c/0x80
> [  135.295284]  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> [...]

Applied, thanks!

[1/1] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0
      commit: 29a5b8a137ac8eb410cc823653a29ac0e7b7e1b0

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>