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Date:   Tue, 12 Jun 2018 13:04:00 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 06/10] e2fsck: Handle s_inodes_count corruption properly

On Jun 12, 2018, at 3:53 AM, Jan Kara <jack@...e.cz> wrote:
> 
> When s_inodes_count would overflow given number of groups and inodes per
> group, we cannot currently fix the breakage in e2fsck as that requires
> trimming number of groups or inodes per group which both means data &
> inode migration etc. Just trimming sb->s_inodes_count is not enough as
> kernel's inode allocation code is not able to handle filesystems where
> not all inodes in the last group are usable. So don't pretend we can fix
> s_inodes_count overflow by just trimming the s_inodes_count value.
> 
> When s_inodes_count is just wrong but will not overflow, let's fix it.
> Also move this check before we use s_inodes_count for checking
> s_first_ino.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>

I guess that still leaves an open issue of what a user can do if the
superblock (correctly or incorrectly) has groups * inodes_per_group
that overflows 2^32, since it seems e2fsck would abort in that case.

I'd think that one option would be to reduce the group count until
the number of inodes < 2^32, which might lose some files at the end
of the filesystem, but more likely would not lose anything since the
kernel would have written those inodes into the wrong place anyway.

The existing code takes the approach of truncating the last group,
which at least makes the filesystem usable again, though it risks
corrupting inode #1 (EXT2_BAD_INO) on older kernels should the last
inode be allocated.  That probably isn't a huge danger in the end.

Cheers, Andreas

> ---
> e2fsck/problem.c |  5 +++++
> e2fsck/problem.h |  2 ++
> e2fsck/super.c   | 27 ++++++++++++++++-----------
> 3 files changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/e2fsck/problem.c b/e2fsck/problem.c
> index edc9d51fcf31..8de558edc5dd 100644
> --- a/e2fsck/problem.c
> +++ b/e2fsck/problem.c
> @@ -184,6 +184,11 @@ static struct e2fsck_problem problem_table[] = {
> 	  N_("@i count in @S is %i, @s %j.\n"),
> 	  PROMPT_FIX, 0 },
> 
> +	/* Too many inodes in the filesystem */
> +	{ PR_0_INODE_COUNT_BIG,
> +	  N_("@S would have too many inodes (%N).\n"),
> +	  PROMPT_NONE, PR_AFTER_CODE, PR_0_SB_CORRUPT },
> +
> 	{ PR_0_HURD_CLEAR_FILETYPE,
> 	  N_("The Hurd does not support the filetype feature.\n"),
> 	  PROMPT_CLEAR, 0 },
> diff --git a/e2fsck/problem.h b/e2fsck/problem.h
> index 482d111a0f2c..b6bca668bb1b 100644
> --- a/e2fsck/problem.h
> +++ b/e2fsck/problem.h
> @@ -282,6 +282,8 @@ struct problem_context {
> /* Invalid quota inode number */
> #define PR_0_INVALID_QUOTA_INO			0x00004F
> 
> +/* Inode count in the superblock incorrect */
> +#define PR_0_INODE_COUNT_BIG			0x000050
> 
> /*
>  * Pass 1 errors
> diff --git a/e2fsck/super.c b/e2fsck/super.c
> index 9c0e0e7b35b4..60a19a7e2767 100644
> --- a/e2fsck/super.c
> +++ b/e2fsck/super.c
> @@ -646,6 +646,22 @@ void check_super_block(e2fsck_t ctx)
> 	check_super_value(ctx, "desc_size",
> 			  sb->s_desc_size, MAX_CHECK | LOG2_CHECK, 0,
> 			  EXT2_MAX_DESC_SIZE);
> +
> +	should_be = (__u64)sb->s_inodes_per_group * fs->group_desc_count;
> +	if (should_be > ~0U) {
> +		pctx.num = should_be;
> +		fix_problem(ctx, PR_0_INODE_COUNT_BIG, &pctx);
> +		ctx->flags |= E2F_FLAG_ABORT;
> +		return;
> +	}
> +	if (sb->s_inodes_count != should_be) {
> +		pctx.ino = sb->s_inodes_count;
> +		pctx.ino2 = should_be;
> +		if (fix_problem(ctx, PR_0_INODE_COUNT_WRONG, &pctx)) {
> +			sb->s_inodes_count = should_be;
> +			ext2fs_mark_super_dirty(fs);
> +		}
> +	}
> 	if (sb->s_rev_level > EXT2_GOOD_OLD_REV)
> 		check_super_value(ctx, "first_ino", sb->s_first_ino,
> 				  MIN_CHECK | MAX_CHECK,
> @@ -683,17 +699,6 @@ void check_super_block(e2fsck_t ctx)
> 		return;
> 	}
> 
> -	should_be = (blk64_t)sb->s_inodes_per_group * fs->group_desc_count;
> -	if (should_be > UINT_MAX)
> -		should_be = UINT_MAX;
> -	if (sb->s_inodes_count != should_be) {
> -		pctx.ino = sb->s_inodes_count;
> -		pctx.ino2 = should_be;
> -		if (fix_problem(ctx, PR_0_INODE_COUNT_WRONG, &pctx)) {
> -			sb->s_inodes_count = should_be;
> -			ext2fs_mark_super_dirty(fs);
> -		}
> -	}
> 	if (EXT2_INODE_SIZE(sb) > EXT2_GOOD_OLD_INODE_SIZE) {
> 		unsigned min =
> 			sizeof(((struct ext2_inode_large *) 0)->i_extra_isize) +
> --
> 2.13.7
> 


Cheers, Andreas






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