Re: [PATCH net v2] ethtool: fix potential userspace buffer overflow

[David Miller <davem@davemloft.net>]

From: Vivien Didelot <vivien.didelot@gmail.com>
Date: Mon,  3 Jun 2019 16:57:13 -0400

> ethtool_get_regs() allocates a buffer of size ops->get_regs_len(),
> and pass it to the kernel driver via ops->get_regs() for filling.
> 
> There is no restriction about what the kernel drivers can or cannot do
> with the open ethtool_regs structure. They usually set regs->version
> and ignore regs->len or set it to the same size as ops->get_regs_len().
> 
> But if userspace allocates a smaller buffer for the registers dump,
> we would cause a userspace buffer overflow in the final copy_to_user()
> call, which uses the regs.len value potentially reset by the driver.
> 
> To fix this, make this case obvious and store regs.len before calling
> ops->get_regs(), to only copy as much data as requested by userspace,
> up to the value returned by ops->get_regs_len().
> 
> While at it, remove the redundant check for non-null regbuf.
> 
> Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>

Applied and queued up for -stable, thanks.