linux-ext4 - Re: [PATCH v2] e2fsck: Fix access after free for dx

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Date:   Sun, 5 Nov 2017 22:49:55 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     Artem Blagodarenko <artem.blagodarenko@...il.com>
Cc:     linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] e2fsck: Fix access after free for dx_db structure

On Nov 4, 2017, at 11:22 AM, Artem Blagodarenko <artem.blagodarenko@...il.com> wrote:
> 
> dx_db structure is freed after fixing of PR_2_HTREE_BAD_ROOT
> problem. Next code block use this structure to unerstand if leaf
> is beeng processed.
> 
> If dx_db is freed, then root block is being processed and if_leaf
> need to be set to 0.
> 
> Signed-off-by: Artem Blagodarenko <artem.blagodarenko@...il.com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> ---
> e2fsck/pass2.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/e2fsck/pass2.c b/e2fsck/pass2.c
> index 09c16179..1b0504c8 100644
> --- a/e2fsck/pass2.c
> +++ b/e2fsck/pass2.c
> @@ -1095,7 +1095,7 @@ inline_read_fail:
> 			    fix_problem(ctx, PR_2_HTREE_BAD_ROOT, &cd->pctx)) {
> 				clear_htree(ctx, ino);
> 				dx_dir->numblocks = 0;
> -				dx_db = 0;
> +				dx_db = NULL;
> 			}
> 			dx_dir->hashversion = root->hash_version;
> 			if ((dx_dir->hashversion <= EXT2_HASH_TEA) &&
> @@ -1107,9 +1107,10 @@ inline_read_fail:
> 			   (ext2fs_dirent_name_len(dirent) == 0) &&
> 			   (ext2fs_le16_to_cpu(limit->limit) ==
> 			    ((fs->blocksize - (8 + dx_csum_size)) /
> -			     sizeof(struct ext2_dx_entry))))
> +			     sizeof(struct ext2_dx_entry)))) {
> 			dx_db->type = DX_DIRBLOCK_NODE;
> -		is_leaf = (dx_db->type == DX_DIRBLOCK_LEAF);
> +		}
> +		is_leaf = dx_db ? (dx_db->type == DX_DIRBLOCK_LEAF) : 0;
> 	}
> out_htree:
> 
> --
> 2.13.5 (Apple Git-94)
> 


Cheers, Andreas






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