Re: [PATCH] f2fs: fix to avoid memory leakage in f2fs_listxattr

[Chao Yu <yuchao0@huawei.com>]

Hi Randall,

On 2019/10/9 11:20, Randall Huang wrote:
> In f2fs_listxattr, there is no boundary check before
> memcpy e_name to buffer.
> If the e_name_len is corrupted,
> unexpected memory contents may be returned to the buffer.
> 
> Signed-off-by: Randall Huang <huangrandall@google.com>
> ---
>  fs/f2fs/xattr.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
> index b32c45621679..acc3663970cd 100644
> --- a/fs/f2fs/xattr.c
> +++ b/fs/f2fs/xattr.c
> @@ -538,8 +538,9 @@ int f2fs_getxattr(struct inode *inode, int index, const char *name,
>  ssize_t f2fs_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
>  {
>  	struct inode *inode = d_inode(dentry);
> +	nid_t xnid = F2FS_I(inode)->i_xattr_nid;
>  	struct f2fs_xattr_entry *entry;
> -	void *base_addr;
> +	void *base_addr, *last_base_addr;
>  	int error = 0;
>  	size_t rest = buffer_size;
>  
> @@ -549,6 +550,8 @@ ssize_t f2fs_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
>  	if (error)
>  		return error;
>  
> +	last_base_addr = (void *)base_addr + XATTR_SIZE(xnid, inode);
> +
>  	list_for_each_xattr(entry, base_addr) {
>  		const struct xattr_handler *handler =
>  			f2fs_xattr_handler(entry->e_name_index);
> @@ -559,6 +562,15 @@ ssize_t f2fs_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
>  		if (!handler || (handler->list && !handler->list(dentry)))
>  			continue;
>  
> +		if ((void *)(entry) + sizeof(__u32) > last_base_addr ||
> +			(void *)XATTR_NEXT_ENTRY(entry) > last_base_addr) {
> +			f2fs_err(F2FS_I_SB(inode), "inode (%lu) has corrupted xattr",
> +						inode->i_ino);
> +			set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
> +			error = -EFSCORRUPTED;
> +			goto cleanup;
> +		}

Could you relocate sanity check to the place before we check handler? As I'm
thinking we should always check validation of current entry before using its
field (entry->index).

Thanks,

> +
>  		prefix = xattr_prefix(handler);
>  		prefix_len = strlen(prefix);
>  		size = prefix_len + entry->e_name_len + 1;
>