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SubjectRe: build_path_from_dentry_optional_prefix() may schedule from invalid context
On Mon, Sep 30, 2019 at 10:32:16AM -0700, Pavel Shilovsky wrote:
> сб, 21 сент. 2019 г. в 15:38, Al Viro <viro@zeniv.linux.org.uk>:

> > IOW, kindly lose that nonsense. More importantly, why bother
> > with that kmalloc()? Just __getname() in the very beginning
> > and __putname() on failure (and for freeing the result afterwards).
> >
> > What's more, you are open-coding dentry_path_raw(), badly.
> > The only differences are
> > * use of dirsep instead of '/' and
> > * a prefix slapped in the beginning.
> >
> > I'm fairly sure that
> > char *buf = __getname();
> > char *s;
> >
> > *to_free = NULL;
> > if (unlikely(!buf))
> > return NULL;
> >
> > s = dentry_path_raw(dentry, buf, PATH_MAX);
> > if (IS_ERR(s) || s < buf + prefix_len)
> > __putname(buf);
> > return NULL; // assuming that you don't care about details
> > }
> >
> > if (dirsep != '/') {
> > char *p = s;
> > while ((p = strchr(p, '/')) != NULL)
> > *p++ = dirsep;
> > }
> >
> > s -= prefix_len;
> > memcpy(s, prefix, prefix_len);
> >
> > *to_free = buf;
> > return s;
> >
> > would end up being faster, not to mention much easier to understand.
> > With the caller expected to pass &to_free among the arguments and
> > __putname() it once it's done.
> >
> > Or just do __getname() in the caller and pass it to the function -
> > in that case freeing (in all cases) would be up to the caller.
>
> Thanks for pointing this out. Someone should look at this closely and
> clean it up.

Could you take a look through vfs.git#misc.cifs?

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