Re: [PATCH net-next] ethtool: do not use regs->len after ops->get_regs
From: Michal Kubecek <hidden>
Date: 2019-05-31 06:54:35
Also in:
lkml
On Thu, May 30, 2019 at 07:54:50PM -0400, Vivien Didelot wrote:
quoted hunk ↗ jump to hunk
The kernel 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 regs->len member. Drivers usually ignore it or set the same size again. However, ethtool_get_regs() must not use this value when copying the buffer back to the user, because userspace may have allocated a smaller buffer. For instance ethtool does that when dumping the raw registers directly into a fixed-size file. Software may still make use of the regs->len value updated by the kernel driver, but ethtool_get_regs() must use the original regs->len given by userspace, up to ops->get_regs_len(), when copying the buffer. Also no need to check regbuf twice. Signed-off-by: Vivien Didelot <redacted> --- net/core/ethtool.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)diff --git a/net/core/ethtool.c b/net/core/ethtool.c index 4a593853cbf2..8f95c7b7cafe 100644 --- a/net/core/ethtool.c +++ b/net/core/ethtool.c@@ -1338,38 +1338,40 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev, static int ethtool_get_regs(struct net_device *dev, char __user *useraddr) { struct ethtool_regs regs; const struct ethtool_ops *ops = dev->ethtool_ops; void *regbuf; int reglen, ret; if (!ops->get_regs || !ops->get_regs_len) return -EOPNOTSUPP; if (copy_from_user(®s, useraddr, sizeof(regs))) return -EFAULT; reglen = ops->get_regs_len(dev); if (reglen <= 0) return reglen; if (regs.len > reglen) regs.len = reglen; + else + reglen = regs.len;
This seems wrong. Most drivers do not check regs.len in their get_regs() handler (I'm not sure if there are any that do) and simply write as much data as they have. Thus if userspace passes too short regs.len, this would replace overflow of a userspace buffer for few drivers by overflow of a kernel buffer for (almost) all drivers. So while we should use the original regs.len from userspace for final copy_to_user(), we have to allocate the buffer for driver ->get_regs() callback with size returned by its ->get_regs_len() callback. Michal Kubecek
regbuf = vzalloc(reglen); if (!regbuf) return -ENOMEM; ops->get_regs(dev, ®s, regbuf); ret = -EFAULT; if (copy_to_user(useraddr, ®s, sizeof(regs))) goto out; useraddr += offsetof(struct ethtool_regs, data); - if (regbuf && copy_to_user(useraddr, regbuf, regs.len)) + if (copy_to_user(useraddr, regbuf, reglen)) goto out; ret = 0; out: vfree(regbuf); return ret; } -- 2.21.0