Re: [PATCH] char: tpm: tpm-buf: Fix uninitialized return values in read helpers

[Stefano Garzarella]

On Thu, Apr 10, 2025 at 09:14:58AM +0300, Jarkko Sakkinen wrote:
> On Thu, Apr 10, 2025 at 02:25:36AM +0530, Purva Yeshi wrote:
> > Fix Smatch-detected error:
> > drivers/char/tpm/tpm-buf.c:208 tpm_buf_read_u8() error:
> > uninitialized symbol 'value'.
> > drivers/char/tpm/tpm-buf.c:225 tpm_buf_read_u16() error:
> > uninitialized symbol 'value'.
> > drivers/char/tpm/tpm-buf.c:242 tpm_buf_read_u32() error:
> > uninitialized symbol 'value'.
> >
> > Call tpm_buf_read() to populate value but do not check its return
> > status. If the read fails, value remains uninitialized, causing
> > undefined behavior when returned or processed.
> >
> > Initialize value to zero to ensure a defined return even if
> > tpm_buf_read() fails, avoiding undefined behavior from using
> > an uninitialized variable.
>
> How does tpm_buf_read() fail?

If TPM_BUF_BOUNDARY_ERROR is set (or we are setting it), we are 
effectively returning random stack bytes to the caller.
Could this be a problem?

If it is, maybe instead of this patch, we could set `*output` to zero in 
the error path of tpm_buf_read(). Or return an error from tpm_buf_read() 
so callers can return 0 or whatever they want.

Thanks,
Stefano