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ethtool: fix potential userspace buffer overflow

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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>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vivien Didelot 2019-06-03 16:57:13 -04:00 committed by David S. Miller
parent 0a8dd9f67c
commit 0ee4e76937
1 changed files with 4 additions and 1 deletions
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5
net/core/ethtool.c
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@ -1359,13 +1359,16 @@ static int ethtool_get_regs(struct net_device *dev, char __user *useraddr)
if (!regbuf)
return -ENOMEM;
if (regs.len < reglen)
reglen = regs.len;
ops->get_regs(dev, &regs, regbuf);
ret = -EFAULT;
if (copy_to_user(useraddr, &regs, 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;