Re: [PATCH] ext4: fix use-after-free Read in ext4_find_extent for bigalloc + inline

[Tudor Ambarus <tudor.ambarus@gmail.com>]

On 04.01.2023 09:15, Ye Bin wrote:
> From: Ye Bin <yebin10@huawei.com>
> 
> Syzbot found the following issue:
> loop0: detected capacity change from 0 to 2048
> EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 without journal. Quota mode: none.
> ==================================================================
> BUG: KASAN: use-after-free in ext4_ext_binsearch_idx fs/ext4/extents.c:768 [inline]
> BUG: KASAN: use-after-free in ext4_find_extent+0x76e/0xd90 fs/ext4/extents.c:931
> Read of size 4 at addr ffff888073644750 by task syz-executor420/5067
> 
> CPU: 0 PID: 5067 Comm: syz-executor420 Not tainted 6.2.0-rc1-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:88 [inline]
>   dump_stack_lvl+0x1b1/0x290 lib/dump_stack.c:106
>   print_address_description+0x74/0x340 mm/kasan/report.c:306
>   print_report+0x107/0x1f0 mm/kasan/report.c:417
>   kasan_report+0xcd/0x100 mm/kasan/report.c:517
>   ext4_ext_binsearch_idx fs/ext4/extents.c:768 [inline]
>   ext4_find_extent+0x76e/0xd90 fs/ext4/extents.c:931
>   ext4_clu_mapped+0x117/0x970 fs/ext4/extents.c:5809
>   ext4_insert_delayed_block fs/ext4/inode.c:1696 [inline]
>   ext4_da_map_blocks fs/ext4/inode.c:1806 [inline]
>   ext4_da_get_block_prep+0x9e8/0x13c0 fs/ext4/inode.c:1870
>   ext4_block_write_begin+0x6a8/0x2290 fs/ext4/inode.c:1098
>   ext4_da_write_begin+0x539/0x760 fs/ext4/inode.c:3082
>   generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772
>   ext4_buffered_write_iter+0x122/0x3a0 fs/ext4/file.c:285
>   ext4_file_write_iter+0x1d0/0x18f0
>   call_write_iter include/linux/fs.h:2186 [inline]
>   new_sync_write fs/read_write.c:491 [inline]
>   vfs_write+0x7dc/0xc50 fs/read_write.c:584
>   ksys_write+0x177/0x2a0 fs/read_write.c:637
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f4b7a9737b9
> RSP: 002b:00007ffc5cac3668 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4b7a9737b9
> RDX: 00000000175d9003 RSI: 0000000020000200 RDI: 0000000000000004
> RBP: 00007f4b7a933050 R08: 0000000000000000 R09: 0000000000000000
> R10: 000000000000079f R11: 0000000000000246 R12: 00007f4b7a9330e0
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>   </TASK>
> 
> Above issue is happens when enable bigalloc and inline data feature. As
> commit 131294c35ed6 fixed delayed allocation bug in ext4_clu_mapped for
> bigalloc + inline. But it only resolved issue when has inline data, if
> inline data has been converted to extent(ext4_da_convert_inline_data_to_extent)
> before writepages, there is no EXT4_STATE_MAY_INLINE_DATA flag. However
> i_data is still store inline data in this scene. Then will trigger UAF
> when find extent.
> To resolve above issue, there is need to add judge "ext4_has_inline_data(inode)"
> in ext4_clu_mapped().
> 
> Reported-by: syzbot+bf4bb7731ef73b83a3b4@syzkaller.appspotmail.com
> Fixes: 131294c35ed6 ("ext4: fix delayed allocation bug in ext4_clu_mapped for bigalloc + inline")
> Signed-off-by: Ye Bin <yebin10@huawei.com>


This also fixes the problem that I tried to address with the superficial
patch at
https://lore.kernel.org/linux-ext4/Y69IaMqZvnGk5skX@mit.edu/T/#t

Tested-by: Tudor Ambarus <tudor.ambarus@linaro.org>

> ---
>   fs/ext4/extents.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 9de1c9d1a13d..ee5acf2bd5e6 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -5802,7 +5802,8 @@ int ext4_clu_mapped(struct inode *inode, ext4_lblk_t lclu)
>   	 * mapped - no physical clusters have been allocated, and the
>   	 * file has no extents
>   	 */
> -	if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA))
> +	if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) ||
> +	    ext4_has_inline_data(inode))
>   		return 0;
>   
>   	/* search for the extent closest to the first block in the cluster */