linux-kernel - Re: [PATCH v5] cifs: Fix copy_to

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Message-ID: <CAH2r5mvws19ho44YJDROdNUy3FtWfxyVE8QcbCTbFJ_VWYNQ9Q@mail.gmail.com>
Date: Tue, 7 Oct 2025 13:41:06 -0500
From: Steve French <smfrench@...il.com>
To: Fushuai Wang <wangfushuai@...du.com>, David Howells <dhowells@...hat.com>
Cc: pc@...guebit.org, ronniesahlberg@...il.com, sprasad@...rosoft.com, 
	tom@...pey.com, bharathsm@...rosoft.com, Markus.Elfring@....de, 
	linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] cifs: Fix copy_to_iter return value check

David suggested fixing this line:

 +                       return -1;

to

 +                       return -EIO;

which makes sense to me since returning -1 could be confusing.

On Tue, Oct 7, 2025 at 3:27 AM Fushuai Wang <wangfushuai@...du.com> wrote:
>
> The return value of copy_to_iter() function will never be negative,
> it is the number of bytes copied, or zero if nothing was copied.
> Update the check to treat 0 as an error, and return -1 in that case.
>
> Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
> Signed-off-by: Fushuai Wang <wangfushuai@...du.com>
> ---
> v5: no code changes, only improve commit format
> v4: no code changes, only add version description
> v3: use size_t type for (copied) and check for (copied == 0) as error.
> v2: use (!length) check for error condition.
> v1: use (length <= 0) check for error condition.
>
>  fs/smb/client/smb2ops.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
> index 058050f744c0..ac8a5bd6aec4 100644
> --- a/fs/smb/client/smb2ops.c
> +++ b/fs/smb/client/smb2ops.c
> @@ -4650,7 +4650,7 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
>         unsigned int pad_len;
>         struct cifs_io_subrequest *rdata = mid->callback_data;
>         struct smb2_hdr *shdr = (struct smb2_hdr *)buf;
> -       int length;
> +       size_t copied;
>         bool use_rdma_mr = false;
>
>         if (shdr->Command != SMB2_READ) {
> @@ -4763,10 +4763,10 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
>         } else if (buf_len >= data_offset + data_len) {
>                 /* read response payload is in buf */
>                 WARN_ONCE(buffer, "read data can be either in buf or in buffer");
> -               length = copy_to_iter(buf + data_offset, data_len, &rdata->subreq.io_iter);
> -               if (length < 0)
> -                       return length;
> -               rdata->got_bytes = data_len;
> +               copied = copy_to_iter(buf + data_offset, data_len, &rdata->subreq.io_iter);
> +               if (copied == 0)
> +                       return -1;
> +               rdata->got_bytes = copied;
>         } else {
>                 /* read response payload cannot be in both buf and pages */
>                 WARN_ONCE(1, "buf can not contain only a part of read data");

> --
> 2.36.1
>
>


--
Thanks,

Steve