lkml.org 
[lkml]   [2022]   [Aug]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v2] ext4: fix bug in extents parsing when eh_entries == 0 and eh_depth > 0
From
Hi Luís,

On 8/12/2022 6:53 PM, 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
>
> This patch simply adds an extra check in __ext4_ext_check(), verifying that
> eh_entries is not 0 when eh_depth is > 0.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215941
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216283
> Cc: Baokun Li <libaokun1@huawei.com>
> Signed-off-by: Luís Henriques <lhenriques@suse.de>
> ---
> fs/ext4/extents.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> Hi!
>
> Baokun's feedback showed me that I had a partial understanding of the
> problem. Thus, I'm sending v2 which pretty much uses Baokun's suggestion
> and simplifies the solution. I've also added the link to the 2nd bugzilla
> to the commit text.
>
> Cheers,
> --
> Luís
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 53cfe2c681c4..a5457ac1999c 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -460,6 +460,11 @@ static int __ext4_ext_check(const char *function, unsigned int line,
> error_msg = "invalid eh_entries";
> goto corrupted;
> }
> + if (unlikely((le16_to_cpu(eh->eh_entries) == 0) &&
> + (le16_to_cpu(eh->eh_depth > 0)))) {

The parentheses are misplaced, and le16_to_cpu is not needed here.

> + error_msg = "eh_entries is 0 but eh_depth is > 0";
> + goto corrupted;
> + }
> if (!ext4_valid_extent_entries(inode, eh, lblk, &pblk, depth)) {
> error_msg = "invalid extent entries";
> goto corrupted;
> .

--
With Best Regards,
Baokun Li

\
 
 \ /
  Last update: 2022-08-12 14:51    [W:0.048 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site