Re: [PATCH] Possible race in sysfs_read_file() and sysfs_write_file()

From: Simon Derr (Simon.Derr_at_bull.net)
Date: 09/03/04

  • Next message: William Lee Irwin III: "Re: [1/4] standardize bit waiting data type" 
    Date:	Fri, 3 Sep 2004 11:39:02 +0200 (DFT)
To: Simon Derr <Simon.Derr@bull.net>

    On Fri, 3 Sep 2004, Simon Derr wrote:

    > On Thu, 2 Sep 2004, Andrew Morton wrote:
    >
    > > Simon Derr <Simon.Derr@bull.net> wrote:
    > > >
    > > > @@ -140,13 +145,17 @@
    > > > struct sysfs_buffer * buffer = file->private_data;
    > > > ssize_t retval = 0;
    > > >
    > > > - if (!*ppos) {
    > > > + down(&buffer->sem);
    > > > + if ((!*ppos) || (!buffer->page)) {
    > > > if ((retval = fill_read_buffer(file->f_dentry,buffer)))
    > > > - return retval;
    > > > + goto out;
    > >
    > > Why are we testing *ppos at all in here?
    >
    > And if we open a sysfs file with O_RDWR, and write() into it, then this is
    > needed if we want to read(), because else the buffer will have been
    > allocated, but ops->show() not called. I'm not too sure about this being
    > useful either.

    Hmmm...
    We are still screwed if we read at offset >0 after a write.

    Possible fix would be to add a 'dirty' flag to the sysfs_buffer when
    write() is called, so we force a call to fill_read_buffer() on the next
    read().

    Or maybe simply forbid O_RDWR open() ? Are they of any use ?
    -
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