Frederick Lawler [off-list ref] 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 <redacted>

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 <redacted>