Re: [PATCH v2 2/2] ext4: fix bug_on in __es_tree_search caused by wrong boot loader inode

[Jan Kara]

On Fri 21-10-22 12:07:31, Baokun Li wrote:
> We got a issue as fllows:
> ==================================================================
>  kernel BUG at fs/ext4/extents_status.c:203!
>  invalid opcode: 0000 [#1] PREEMPT SMP
>  CPU: 1 PID: 945 Comm: cat Not tainted 6.0.0-next-20221007-dirty #349
>  RIP: 0010:ext4_es_end.isra.0+0x34/0x42
>  RSP: 0018:ffffc9000143b768 EFLAGS: 00010203
>  RAX: 0000000000000000 RBX: ffff8881769cd0b8 RCX: 0000000000000000
>  RDX: 0000000000000000 RSI: ffffffff8fc27cf7 RDI: 00000000ffffffff
>  RBP: ffff8881769cd0bc R08: 0000000000000000 R09: ffffc9000143b5f8
>  R10: 0000000000000001 R11: 0000000000000001 R12: ffff8881769cd0a0
>  R13: ffff8881768e5668 R14: 00000000768e52f0 R15: 0000000000000000
>  FS: 00007f359f7f05c0(0000)GS:ffff88842fd00000(0000)knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 00007f359f5a2000 CR3: 000000017130c000 CR4: 00000000000006e0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  Call Trace:
>   <TASK>
>   __es_tree_search.isra.0+0x6d/0xf5
>   ext4_es_cache_extent+0xfa/0x230
>   ext4_cache_extents+0xd2/0x110
>   ext4_find_extent+0x5d5/0x8c0
>   ext4_ext_map_blocks+0x9c/0x1d30
>   ext4_map_blocks+0x431/0xa50
>   ext4_mpage_readpages+0x48e/0xe40
>   ext4_readahead+0x47/0x50
>   read_pages+0x82/0x530
>   page_cache_ra_unbounded+0x199/0x2a0
>   do_page_cache_ra+0x47/0x70
>   page_cache_ra_order+0x242/0x400
>   ondemand_readahead+0x1e8/0x4b0
>   page_cache_sync_ra+0xf4/0x110
>   filemap_get_pages+0x131/0xb20
>   filemap_read+0xda/0x4b0
>   generic_file_read_iter+0x13a/0x250
>   ext4_file_read_iter+0x59/0x1d0
>   vfs_read+0x28f/0x460
>   ksys_read+0x73/0x160
>   __x64_sys_read+0x1e/0x30
>   do_syscall_64+0x35/0x80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>   </TASK>
> ==================================================================
> 
> In the above issue, ioctl invokes the swap_inode_boot_loader function to
> swap inode<5> and inode<12>. However, inode<5> contain incorrect imode and
> disordered extents, and i_nlink is set to 1. The extents check for inode in
> the ext4_iget function can be bypassed bacause 5 is EXT4_BOOT_LOADER_INO.
> While links_count is set to 1, the extents are not initialized in
> swap_inode_boot_loader. After the ioctl command is executed successfully,
> the extents are swapped to inode<12>, in this case, run the `cat` command
> to view inode<12>. And Bug_ON is triggered due to the incorrect extents.
> 
> When the boot loader inode is not initialized, its imode can be one of the
> following:
> 1) the imode is a bad type, which is marked as bad_inode in ext4_iget and
>    set to S_IFREG.
> 2) the imode is good type but not S_IFREG.
> 3) the imode is S_IFREG.
> 
> The BUG_ON may be triggered by bypassing the check in cases 1 and 2.
> Therefore, when the boot loader inode is bad_inode or its imode is not
> S_IFREG, initialize the inode to avoid triggering the BUG.
> 
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>

Grepping for calls to ext4_iget() in the ext4 code shows there are many
more places that will get unhappy (and crash) when ext4_iget() returns a
bad inode. In fact, I didn't find a place when returning bad inode would be
useful for anything. So why don't we just return EFSCORRUPTED instead of
returning a bad inode?

								Honza

> ---
>  fs/ext4/ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index ded535535b27..c41210706ea7 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -425,7 +425,7 @@ static long swap_inode_boot_loader(struct super_block *sb,
>  	/* Protect extent tree against block allocations via delalloc */
>  	ext4_double_down_write_data_sem(inode, inode_bl);
>  
> -	if (inode_bl->i_nlink == 0) {
> +	if (is_bad_inode(inode_bl) || !S_ISREG(inode_bl->i_mode)) {
>  		/* this inode has never been used as a BOOT_LOADER */
>  		set_nlink(inode_bl, 1);
>  		i_uid_write(inode_bl, 0);
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR