On Friday, November 01, 2013 22:24:12 Tetsuo Handa wrote:
> Jim Lieb wrote:
> > Subsequent uses look like:
> > use_creds(cached fd);
> >
> > followed by
> >
> > open/creat/mknod/write
> >
> > followed by
> >
> > use_creds(-1);
>
> Are you aware that calling commit_creds() is prohibitted between
> override_creds() and revert_creds() ?
>
> If the caller does some operation that calls commit_creds() (like
> example below), the kernel triggers BUG().
Yes, I do. I caught this in an early pass. I only use override_creds() and
revert_creds().
>
> ---------- example module start ----------
> #include <linux/module.h>
> #include <linux/cred.h>
> #include <linux/fs.h>
> #include <linux/file.h>
>
> static int __init test_init(void)
> {
> { /* switch_creds() syscall */
> struct fd f = fdget(0);
> if (!f.file)
> return -EBADF;
> put_cred(override_creds(f.file->f_cred));
> fdput(f);
> }
> { /* something that calls commit_creds() */
> struct cred *cred = prepare_creds();
> if (cred)
> commit_creds(cred);
> }
> return 0;
> }
>
> static void test_exit(void)
> {
> }
>
> module_init(test_init);
> module_exit(test_exit);
> MODULE_LICENSE("GPL");
> ---------- example module end ----------
>
> Since nobody can guarantee that the caller of switch_creds() never does
> some operation that calls commit_creds(), I don't think switch_creds()
> based on override_creds() will work.
--
Jim Lieb
Linux Systems Engineer
Panasas Inc.
"If ease of use was the only requirement, we would all be riding tricycles"
- Douglas Engelbart 1925–2013
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