linux-ext4 - Re: [PATCH 5/7] e2fsck: avoid out-of-bounds write for very deep extent trees

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Date:   Tue, 7 Jun 2022 15:53:40 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Nils Bars <nils.bars@....de>,
        Moritz Schlögel <moritz.schloegel@....de>,
        Nico Schiller <nico.schiller@....de>
Subject: Re: [PATCH 5/7] e2fsck: avoid out-of-bounds write for very deep
 extent trees

On Tue, Jun 07, 2022 at 12:24:42AM -0400, Theodore Ts'o wrote:
> The kernel doesn't support extent trees deeper than 5
> (EXT4_MAX_EXTENT_DEPTH).  For this reason we only maintain the extent
> tree statistics for 5 levels.  Avoid out-of-bounds writes and reads if
> the extent tree is deeper than this.
> 
> We keep these statistics to determine whether we should rebuild the
> extent tree.  If the extent tree is too deep, we don't need the
> statistics because we should always rebuild the it.

Looks good.

Reviewed-by: Lukas Czerner <lczerner@...hat.com>

> 
> Reported-by: Nils Bars <nils.bars@....de>
> Reported-by: Moritz Schlögel <moritz.schloegel@....de>
> Reported-by: Nico Schiller <nico.schiller@....de>
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> ---
>  e2fsck/extents.c | 10 +++++++++-
>  e2fsck/pass1.c   |  3 ++-
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/e2fsck/extents.c b/e2fsck/extents.c
> index 01879f56..86fe00e7 100644
> --- a/e2fsck/extents.c
> +++ b/e2fsck/extents.c
> @@ -526,7 +526,8 @@ errcode_t e2fsck_check_rebuild_extents(e2fsck_t ctx, ext2_ino_t ino,
>  		 */
>  		if (info.curr_entry == 1 &&
>  		    !(extent.e_flags & EXT2_EXTENT_FLAGS_SECOND_VISIT) &&
> -		    !eti.force_rebuild) {
> +		    !eti.force_rebuild &&
> +		    info.curr_level < MAX_EXTENT_DEPTH_COUNT) {
>  			struct extent_tree_level *etl;
>  
>  			etl = eti.ext_info + info.curr_level;
> @@ -580,6 +581,13 @@ errcode_t e2fsck_should_rebuild_extents(e2fsck_t ctx,
>  	extents_per_block = (ctx->fs->blocksize -
>  			     sizeof(struct ext3_extent_header)) /
>  			    sizeof(struct ext3_extent);
> +
> +	/* If the extent tree is too deep, then rebuild it. */
> +	if (info->max_depth > MAX_EXTENT_DEPTH_COUNT) {
> +		pctx->blk = info->max_depth;
> +		op = PR_1E_CAN_COLLAPSE_EXTENT_TREE;
> +		goto rebuild;
> +	}
>  	/*
>  	 * If we can consolidate a level or shorten the tree, schedule the
>  	 * extent tree to be rebuilt.
> diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
> index 11d7ce93..43972e7c 100644
> --- a/e2fsck/pass1.c
> +++ b/e2fsck/pass1.c
> @@ -2842,7 +2842,8 @@ static void scan_extent_node(e2fsck_t ctx, struct problem_context *pctx,
>  	if (pctx->errcode)
>  		return;
>  	if (!(ctx->options & E2F_OPT_FIXES_ONLY) &&
> -	    !pb->eti.force_rebuild) {
> +	    !pb->eti.force_rebuild &&
> +	    info.curr_level < MAX_EXTENT_DEPTH_COUNT) {
>  		struct extent_tree_level *etl;
>  
>  		etl = pb->eti.ext_info + info.curr_level;
> -- 
> 2.31.0
>