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().
---------- 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.
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