[PATCH v2] cred: Propagate security_prepare_creds() error code

[Jeff Moyer]

Frederick Lawler <fred at cloudflare.com> writes:

> While experimenting with the security_prepare_creds() LSM hook, we
> noticed that our EPERM error code was not propagated up the callstack.
> Instead ENOMEM is always returned.  As a result, some tools may send a
> confusing error message to the user:
>
> $ unshare -rU
> unshare: unshare failed: Cannot allocate memory
>
> A user would think that the system didn't have enough memory, when
> instead the action was denied.
>
> This problem occurs because prepare_creds() and prepare_kernel_cred()
> return NULL when security_prepare_creds() returns an error code. Later,
> functions calling prepare_creds() and prepare_kernel_cred() return
> ENOMEM because they assume that a NULL meant there was no memory
> allocated.
>
> Fix this by propagating an error code from security_prepare_creds() up
> the callstack.
>
> Signed-off-by: Frederick Lawler <fred at cloudflare.com>

The fs/aio.c part looks ok to me.  We should probably also update the
man page for io_submit, though, to document the conditions under which
EPERM can be returned.

Acked-by: Jeff Moyer <jmoyer at redhat.com>