[PATCH] Link count attribute extension

[Damien Miller]

Hi,

Thanks for the patch! Could I ask you to create a bug on
https://bugzilla.mindrot.org/ and attach it so it doesn't get lost?

Thanks,
Damien Miller

On Thu, 2 Jun 2016, Rian Hunter wrote:

> Hello,
> 
> This patch adds client and server support for transmitting the st_nlink field
> across SSH2_FXP_NAME and SSH2_FXP_ATTRS responses.
> 
> Please let me know if there anything I can do to improve this patch. I am
> not subscribed to list so please CC me.
> 
> Index: sftp-common.c
> ===================================================================
> RCS file: /cvs/src/usr.bin/ssh/sftp-common.c,v
> retrieving revision 1.28
> diff -u -r1.28 sftp-common.c
> --- sftp-common.c	20 Jan 2015 23:14:00 -0000	1.28
> +++ sftp-common.c	2 Jun 2016 01:32:02 -0000
> @@ -56,6 +56,8 @@
>  	a->perm = 0;
>  	a->atime = 0;
>  	a->mtime = 0;
> +	a->has_nlink = 0;
> +	a->nlink = 0;
>  }
>  
>  /* Convert from struct stat to filexfer attribs */
> @@ -74,6 +76,9 @@
>  	a->flags |= SSH2_FILEXFER_ATTR_ACMODTIME;
>  	a->atime = st->st_atime;
>  	a->mtime = st->st_mtime;
> +	a->flags |= SSH2_FILEXFER_ATTR_EXTENDED;
> +	a->has_nlink = 1;
> +	a->nlink = st->st_nlink;
>  }
>  
>  /* Convert from filexfer attribs to struct stat */
> @@ -94,6 +99,11 @@
>  		st->st_atime = a->atime;
>  		st->st_mtime = a->mtime;
>  	}
> +	if (a->flags & SSH2_FILEXFER_ATTR_EXTENDED) {
> +		if (a->has_nlink) {
> +			st->st_nlink = a->nlink;
> +		}
> +	}
>  }
>  
>  /* Decode attributes in buffer */
> @@ -138,6 +148,15 @@
>  				return r;
>  			debug3("Got file attribute \"%.100s\" len %zu",
>  			    type, dlen);
> +			if (strcmp(type, SFTP_EXT_ATTR_LINK_COUNT) == 0) {
> +				if (dlen < 8) {
> +					return SSH_ERR_MESSAGE_INCOMPLETE;
> +					free(type);
> +					free(data);
> +				}
> +				a->has_nlink = 1;
> +				a->nlink = PEEK_U64(data);
> +			}
>  			free(type);
>  			free(data);
>  		}
> @@ -170,6 +189,24 @@
>  		if ((r = sshbuf_put_u32(b, a->atime)) != 0 ||
>  		    (r = sshbuf_put_u32(b, a->mtime)) != 0)
>  			return r;
> +	}
> +	if (a->flags & SSH2_FILEXFER_ATTR_EXTENDED) {
> +		u_int32_t count = 0;
> +		if (a->has_nlink) {
> +			count += 1;
> +		}
> +
> +		if (count) {
> +			if ((r = sshbuf_put_u32(b, count)) != 0)
> +				return r;
> +
> +			if (a->has_nlink) {
> +				if ((r = sshbuf_put_cstring(b, SFTP_EXT_ATTR_LINK_COUNT)) != 0 ||
> +				    (r = sshbuf_put_u32(b, 8)) != 0 ||
> +				    (r = sshbuf_put_u64(b, a->nlink)))
> +					return r;
> +			}
> +		}
>  	}
>  	return 0;
>  }
> Index: sftp-common.h
> ===================================================================
> RCS file: /cvs/src/usr.bin/ssh/sftp-common.h,v
> retrieving revision 1.12
> diff -u -r1.12 sftp-common.h
> --- sftp-common.h	14 Jan 2015 13:54:13 -0000	1.12
> +++ sftp-common.h	2 Jun 2016 01:32:02 -0000
> @@ -40,6 +40,8 @@
>  	u_int32_t	perm;
>  	u_int32_t	atime;
>  	u_int32_t	mtime;
> +	u_int32_t	has_nlink;
> +	u_int64_t	nlink;
>  };
>  
>  void	 attrib_clear(Attrib *);
> @@ -50,3 +52,5 @@
>  char	*ls_file(const char *, const struct stat *, int, int);
>  
>  const char *fx2txt(int);
> +
> +#define SFTP_EXT_ATTR_LINK_COUNT "attr-link-count at openssh.com"
> Index: sftp-server.c
> ===================================================================
> RCS file: /cvs/src/usr.bin/ssh/sftp-server.c,v
> retrieving revision 1.109
> diff -u -r1.109 sftp-server.c
> --- sftp-server.c	15 Feb 2016 09:47:49 -0000	1.109
> +++ sftp-server.c	2 Jun 2016 01:32:02 -0000
> @@ -659,6 +659,9 @@
>  	    (r = sshbuf_put_cstring(msg, "1")) != 0 || /* version */
>  	    /* fsync extension */
>  	    (r = sshbuf_put_cstring(msg, "fsync at openssh.com")) != 0 ||
> +	    (r = sshbuf_put_cstring(msg, "1")) != 0 || /* version */
> +	    /* attr link count extension */
> +	    (r = sshbuf_put_cstring(msg, SFTP_EXT_ATTR_LINK_COUNT)) != 0 ||
>  	    (r = sshbuf_put_cstring(msg, "1")) != 0) /* version */
>  		fatal("%s: buffer error: %s", __func__, ssh_err(r));
>  	send_msg(msg);
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