Jim Lieb wrote:
> 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().
Excuse me, but even below example will trigger BUG(). You pack
override_creds() + open() + revert_creds() into one system call so that the
caller of this system call shall not do something that calls commit_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)
{
const struct cred *orig;
{ /* switch_cred() syscall */
struct fd f = fdget(0);
if (!f.file)
return -EBADF;
orig = override_creds(f.file->f_cred);
fdput(f);
}
{ /* something that calls commit_creds() */
struct cred *cred = prepare_creds();
if (cred)
commit_creds(cred);
}
{ /* restore */
revert_creds(orig);
}
return 0;
}
static void test_exit(void)
{
}
module_init(test_init);
module_exit(test_exit);
MODULE_LICENSE("GPL");
---------- example module end ----------
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