Re: [PATCH v3 6/7] erofs: handle long xattr name prefixes properly

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2023/4/11 17:35, Jingbo Xu wrote:
> Make .{list,get}xattr routines adapted to long xattr name prefixes.
> When the bit 7 of erofs_xattr_entry.e_name_index is set, it indicates
> that it refers to a long xattr name prefix.
> 
> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> ---
> v3: introduce infix_len to struct getxattr_iter, and refactor the
> implementation of xattr_entrymatch(), erofs_xattr_long_entrymatch(), and
> xattr_namematch() accordingly.
> 
> The erofs_xattr_long_entrymatch() of v2 version will advance
> it->name.name pointer by pf->infix_len prematurely, as the following
> xattr_namematch() may fail (-ENOATTR) since mismatching.  And then
> it->name.name will be compared with the next xattr entry, while
> it->name.name has been mistakenly modified in the previous round.  This
> will cause -ENOATTR error on the existing xattr.

Yes, please also help add a new erofs-utils testcase for this.

Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang

> 
> ---
>   fs/erofs/xattr.c | 68 +++++++++++++++++++++++++++++++++++++++---------
>   1 file changed, 56 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
> index 684571e83a2c..a04724c816e5 100644
> --- a/fs/erofs/xattr.c
> +++ b/fs/erofs/xattr.c
> @@ -297,17 +297,45 @@ struct getxattr_iter {
>   	struct xattr_iter it;
>   
>   	char *buffer;
> -	int buffer_size, index;
> +	int buffer_size, index, infix_len;
>   	struct qstr name;
>   };
>   
> +static int erofs_xattr_long_entrymatch(struct getxattr_iter *it,
> +				       struct erofs_xattr_entry *entry)
> +{
> +	struct erofs_sb_info *sbi = EROFS_SB(it->it.sb);
> +	struct erofs_xattr_prefix_item *pf = sbi->xattr_prefixes +
> +		(entry->e_name_index & EROFS_XATTR_LONG_PREFIX_MASK);
> +
> +	if (pf >= sbi->xattr_prefixes + sbi->xattr_prefix_count)
> +		return -ENOATTR;
> +
> +	if (it->index != pf->prefix->base_index ||
> +	    it->name.len != entry->e_name_len + pf->infix_len)
> +		return -ENOATTR;
> +
> +	if (memcmp(it->name.name, pf->prefix->infix, pf->infix_len))
> +		return -ENOATTR;
> +
> +	it->infix_len = pf->infix_len;
> +	return 0;
> +}
> +
>   static int xattr_entrymatch(struct xattr_iter *_it,
>   			    struct erofs_xattr_entry *entry)
>   {
>   	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);
>   
> -	return (it->index != entry->e_name_index ||
> -		it->name.len != entry->e_name_len) ? -ENOATTR : 0;
> +	/* should also match the infix for long name prefixes */
> +	if (entry->e_name_index & EROFS_XATTR_LONG_PREFIX)
> +		return erofs_xattr_long_entrymatch(it, entry);
> +
> +	if (it->index != entry->e_name_index ||
> +	    it->name.len != entry->e_name_len)
> +		return -ENOATTR;
> +	it->infix_len = 0;
> +	return 0;
>   }
>   
>   static int xattr_namematch(struct xattr_iter *_it,
> @@ -315,7 +343,9 @@ static int xattr_namematch(struct xattr_iter *_it,
>   {
>   	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);
>   
> -	return memcmp(buf, it->name.name + processed, len) ? -ENOATTR : 0;
> +	if (memcmp(buf, it->name.name + it->infix_len + processed, len))
> +		return -ENOATTR;
> +	return 0;
>   }
>   
>   static int xattr_checkbuffer(struct xattr_iter *_it,
> @@ -487,12 +517,24 @@ static int xattr_entrylist(struct xattr_iter *_it,
>   {
>   	struct listxattr_iter *it =
>   		container_of(_it, struct listxattr_iter, it);
> -	unsigned int prefix_len;
> -	const char *prefix;
> -
> -	const struct xattr_handler *h =
> -		erofs_xattr_handler(entry->e_name_index);
> +	unsigned int base_index = entry->e_name_index;
> +	unsigned int prefix_len, infix_len = 0;
> +	const char *prefix, *infix = NULL;
> +	const struct xattr_handler *h;
> +
> +	if (entry->e_name_index & EROFS_XATTR_LONG_PREFIX) {
> +		struct erofs_sb_info *sbi = EROFS_SB(_it->sb);
> +		struct erofs_xattr_prefix_item *pf = sbi->xattr_prefixes +
> +			(entry->e_name_index & EROFS_XATTR_LONG_PREFIX_MASK);
> +
> +		if (pf >= sbi->xattr_prefixes + sbi->xattr_prefix_count)
> +			return 1;
> +		infix = pf->prefix->infix;
> +		infix_len = pf->infix_len;
> +		base_index = pf->prefix->base_index;
> +	}
>   
> +	h = erofs_xattr_handler(base_index);
>   	if (!h || (h->list && !h->list(it->dentry)))
>   		return 1;
>   
> @@ -500,16 +542,18 @@ static int xattr_entrylist(struct xattr_iter *_it,
>   	prefix_len = strlen(prefix);
>   
>   	if (!it->buffer) {
> -		it->buffer_ofs += prefix_len + entry->e_name_len + 1;
> +		it->buffer_ofs += prefix_len + infix_len +
> +					entry->e_name_len + 1;
>   		return 1;
>   	}
>   
> -	if (it->buffer_ofs + prefix_len
> +	if (it->buffer_ofs + prefix_len + infix_len +
>   		+ entry->e_name_len + 1 > it->buffer_size)
>   		return -ERANGE;
>   
>   	memcpy(it->buffer + it->buffer_ofs, prefix, prefix_len);
> -	it->buffer_ofs += prefix_len;
> +	memcpy(it->buffer + it->buffer_ofs + prefix_len, infix, infix_len);
> +	it->buffer_ofs += prefix_len + infix_len;
>   	return 0;
>   }
>