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Date: Mon, 10 Jun 2019 10:42:29 +0200 From: Michal Kubecek <mkubecek@...e.cz> To: stable@...r.kernel.org Cc: Pavel Machek <pavel@...x.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>, "David S. Miller" <davem@...emloft.net> Subject: Re: [PATCH 4.19 01/51] ethtool: fix potential userspace buffer overflow On Mon, Jun 10, 2019 at 10:21:12AM +0200, Pavel Machek wrote: > Hi! > > > From: Vivien Didelot <vivien.didelot@...il.com> > > > > [ Upstream commit 0ee4e76937d69128a6a66861ba393ebdc2ffc8a2 ] > > > > 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. > > Mainline differs from 4.19-stable here, and while the non-null check > is redundant in -mainline, it does not seem to be redundant in > -stable. > > In stable, if get_regs_len() returns < 0, we'll pass it to vzalloc. Right. :-( I guess we should also pick commit f9fc54d313fa ("ethtool: check the return value of get_regs_len") to stable branches before 5.0. Michal
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