ACK/Cmnt: [PATCH][UBUNTU][SAUCE][SRU][B/F/G/H/I] ext4: fix directory index node split corruption

[Stefan Bader]

On 06.07.21 15:36, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1933074
> 
> [ Note: This was originally sent upstream to linux-ext4 at vger.kernel.org
>    and Ted Tso but didn't seem to make it to the list, presumably as it
>    was marked as SPAM
> 
>    See: http://www.voxelsoft.com/2021/ext4_large_dir_corruption.html ]
> 
> Following commit b5776e7, a trivial sequential write of empty files to
> an empty ext4 file system (with large_dir enabled) fails after just
> over 26 million files. Depending on luck, file creation will give error
> EEXIST or EUCLEAN.
> 
> Commit b5776e7 fixed the no-restart condition so that
> ext4_handle_dirty_dx_node is always called, but it also broke the
> restart condition. This is because when restart=1, the original
> implementation correctly skipped do_split() but b5776e7 clobbered the
> "if(restart)goto journal_error;" logic.
> 
> This complementary change protects do_split() from restart condition,
> making it safe from both current and future ordering of goto statements
> in earlier sections of the code.
> 
> Tested on 5.11.20 with handy testing script:
> 
> i = 0
> while i <= 32000000:
>      print (i)
>      with open('tmpmnt/%d' % i, 'wb') as fout:
>          i += 1
> 
> Google-Bug-Id: 176345532
> Fixes: b5776e7 ("ext4: fix potential htree index checksum corruption")
> Fixes: e08ac99 ("ext4: add largedir feature")
> Signed-off-by: denis at voxelsoft.com
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

As this is not anywhere upstream, yet, we would need to prefix this with 
"UBUNTU: SAUCE" when we apply it. The change does what it explains but more than 
that there is good testing with this.

-Stefan

>   fs/ext4/namei.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 4c37abe..9ad5cc6 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -2432,13 +2432,15 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
>   			goto journal_error;
>   		}
>   	}
> -	de = do_split(handle, dir, &bh, frame, &fname->hinfo);
> -	if (IS_ERR(de)) {
> -		err = PTR_ERR(de);
> +	if (!restart) {
> +		de = do_split(handle, dir, &bh, frame, &fname->hinfo);
> +		if (IS_ERR(de)) {
> +			err = PTR_ERR(de);
> +			goto cleanup;
> +		}
> +		err = add_dirent_to_buf(handle, fname, dir, inode, de, bh);
>   		goto cleanup;
>   	}
> -	err = add_dirent_to_buf(handle, fname, dir, inode, de, bh);
> -	goto cleanup;
>   
>   journal_error:
>   	ext4_std_error(dir->i_sb, err); /* this is a no-op if err == 0 */
> 


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