linux-kernel - Re: [PATCH] seq_file:update file->f_pos when lseek() to m->read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <51D17B76.3060803@gmail.com>
Date:	Mon, 01 Jul 2013 08:52:06 -0400
From:	Dong Fang <yp.fangdong@...il.com>
To:	Jiaxing Wang <hello.wjx@...il.com>
CC:	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] seq_file:update file->f_pos when lseek() to m->read_pos

On 06/29/2013 05:11 AM, Jiaxing Wang wrote:
> After pread(), file->f_pos and m->read_pos get different,
> and lseek() to m->read_pos did not update file->f_pos, then
> a subsequent read may read from a wrong position, the following
> program shows the problem:
>
>      char str1[32] = { 0 };
>      char str2[32] = { 0 };
>      int poffset = 10;
>      int count = 20;
>
>      /*open any seq file*/
>      int fd = open("/proc/modules", O_RDONLY);
>
>      pread(fd, str1, count, poffset);
>      printf("pread:%s\n", str1);
>
>      /*seek to where m->read_pos is*/
>      lseek(fd, poffset+count, SEEK_SET);
>
>      /*supposed to read from poffset+count, but this read from position 0*/
>      read(fd, str2, count);
>      printf("read:%s\n", str2);
>
> Signed-off-by: Jiaxing Wang <hello.wjx@...il.com>
> ---
>   fs/seq_file.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/seq_file.c b/fs/seq_file.c
> index 774c1eb..4b22b26 100644
> --- a/fs/seq_file.c
> +++ b/fs/seq_file.c
> @@ -328,7 +328,8 @@ loff_t seq_lseek(struct file *file, loff_t offset, int whence)
>   				m->read_pos = offset;
>   				retval = file->f_pos = offset;
>   			}
> -		}
> +		} else
> +			file->f_pos = offset;
>   	}
>   	file->f_version = m->version;
>   	mutex_unlock(&m->lock);
>
This does not appear to be a problem, in linux man page, the behaver 
seems clearly defined:

DESCRIPTION
        pread() reads up to count bytes from file descriptor fd at
offset  off-set  (from the start of the file) into the buffer starting
at buf.  The file offset is not changed.
        pwrite() writes up to count bytes from the buffer starting at
buf  to the  file  descriptor  fd  at  offset  offset.   The file
offset is not changed.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/