linux-ext4 - Re: [PATCH 2/7] e2fsck: fix potential out-of-bounds read in inc_ea_inode

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Date:   Tue, 7 Jun 2022 15:30:52 +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 2/7] e2fsck: fix potential out-of-bounds read in
 inc_ea_inode_refs()

On Tue, Jun 07, 2022 at 12:24:39AM -0400, Theodore Ts'o wrote:
> If there isn't enough space for a full extended attribute entry,
> inc_ea_inode_refs() might end up reading beyond the allocated memory
> buffer.

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/pass1.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
> index dde862a8..2a17bb8a 100644
> --- a/e2fsck/pass1.c
> +++ b/e2fsck/pass1.c
> @@ -389,13 +389,13 @@ static problem_t check_large_ea_inode(e2fsck_t ctx,
>  static void inc_ea_inode_refs(e2fsck_t ctx, struct problem_context *pctx,
>  			      struct ext2_ext_attr_entry *first, void *end)
>  {
> -	struct ext2_ext_attr_entry *entry;
> +	struct ext2_ext_attr_entry *entry = first;
> +	struct ext2_ext_attr_entry *np = EXT2_EXT_ATTR_NEXT(entry);
>  
> -	for (entry = first;
> -	     (void *)entry < end && !EXT2_EXT_IS_LAST_ENTRY(entry);
> -	     entry = EXT2_EXT_ATTR_NEXT(entry)) {
> +	while ((void *) entry < end && (void *) np < end &&
> +	       !EXT2_EXT_IS_LAST_ENTRY(entry)) {
>  		if (!entry->e_value_inum)
> -			continue;
> +			goto next;
>  		if (!ctx->ea_inode_refs) {
>  			pctx->errcode = ea_refcount_create(0,
>  							   &ctx->ea_inode_refs);
> @@ -408,6 +408,9 @@ static void inc_ea_inode_refs(e2fsck_t ctx, struct problem_context *pctx,
>  		}
>  		ea_refcount_increment(ctx->ea_inode_refs, entry->e_value_inum,
>  				      0);
> +	next:
> +		entry = np;
> +		np = EXT2_EXT_ATTR_NEXT(entry);
>  	}
>  }
>  
> -- 
> 2.31.0
>