linux-kernel - Re: [PATCH 1/3 v2] fs: ocfs2: Fix possible null-pointer dereferences in ocfs2_xa_prepare

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Date:   Sat, 27 Jul 2019 08:49:57 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, mark@...heh.com,
        jlbec@...lplan.org, Andrew Morton <akpm@...ux-foundation.org>
Cc:     ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3 v2] fs: ocfs2: Fix possible null-pointer dereferences
 in ocfs2_xa_prepare_entry()



On 19/7/26 18:14, Jia-Ju Bai wrote:
> In ocfs2_xa_prepare_entry(), there is an if statement on line 2136 to
> check whether loc->xl_entry is NULL:
>     if (loc->xl_entry)
> 
> When loc->xl_entry is NULL, it is used on line 2158:
>     ocfs2_xa_add_entry(loc, name_hash);
>         loc->xl_entry->xe_name_hash = cpu_to_le32(name_hash);
>         loc->xl_entry->xe_name_offset = cpu_to_le16(loc->xl_size);
> and line 2164:
>     ocfs2_xa_add_namevalue(loc, xi);
>         loc->xl_entry->xe_value_size = cpu_to_le64(xi->xi_value_len);
>         loc->xl_entry->xe_name_len = xi->xi_name_len;
> 
> Thus, possible null-pointer dereferences may occur.
> 
> To fix these bugs, if loc-xl_entry is NULL, ocfs2_xa_prepare_entry()
> abnormally returns with -EINVAL.
> 
> These bugs are found by a static analysis tool STCheck written by us.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>

Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
> ---
> v2:
> * Directly return -EINVAL if loc-xl_entry is NULL.
>   Thank Joseph for helpful advice.
> 
> ---
>  fs/ocfs2/xattr.c | 44 +++++++++++++++++++++++---------------------
>  1 file changed, 23 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> index 385f3aaa2448..4b876c82a35c 100644
> --- a/fs/ocfs2/xattr.c
> +++ b/fs/ocfs2/xattr.c
> @@ -2133,29 +2133,31 @@ static int ocfs2_xa_prepare_entry(struct ocfs2_xa_loc *loc,
>  	if (rc)
>  		goto out;
>  
> -	if (loc->xl_entry) {
> -		if (ocfs2_xa_can_reuse_entry(loc, xi)) {
> -			orig_value_size = loc->xl_entry->xe_value_size;
> -			rc = ocfs2_xa_reuse_entry(loc, xi, ctxt);
> -			if (rc)
> -				goto out;
> -			goto alloc_value;
> -		}
> +	if (!loc->xl_entry) {
> +		rc = -EINVAL;
> +		goto out;
> +	}
>  
> -		if (!ocfs2_xattr_is_local(loc->xl_entry)) {
> -			orig_clusters = ocfs2_xa_value_clusters(loc);
> -			rc = ocfs2_xa_value_truncate(loc, 0, ctxt);
> -			if (rc) {
> -				mlog_errno(rc);
> -				ocfs2_xa_cleanup_value_truncate(loc,
> -								"overwriting",
> -								orig_clusters);
> -				goto out;
> -			}
> +	if (ocfs2_xa_can_reuse_entry(loc, xi)) {
> +		orig_value_size = loc->xl_entry->xe_value_size;
> +		rc = ocfs2_xa_reuse_entry(loc, xi, ctxt);
> +		if (rc)
> +			goto out;
> +		goto alloc_value;
> +	}
> +
> +	if (!ocfs2_xattr_is_local(loc->xl_entry)) {
> +		orig_clusters = ocfs2_xa_value_clusters(loc);
> +		rc = ocfs2_xa_value_truncate(loc, 0, ctxt);
> +		if (rc) {
> +			mlog_errno(rc);
> +			ocfs2_xa_cleanup_value_truncate(loc,
> +							"overwriting",
> +							orig_clusters);
> +			goto out;
>  		}
> -		ocfs2_xa_wipe_namevalue(loc);
> -	} else
> -		ocfs2_xa_add_entry(loc, name_hash);
> +	}
> +	ocfs2_xa_wipe_namevalue(loc);
>  
>  	/*
>  	 * If we get here, we have a blank entry.  Fill it.  We grow our
>