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Subject[PATCH 4.9 62/83] ethtool: fix potential userspace buffer overflow
Date
From: Vivien Didelot <vivien.didelot@gmail.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.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/ethtool.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1390,13 +1390,16 @@ static int ethtool_get_regs(struct net_d
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;


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