[PATCH 4.14 01/35] ethtool: fix potential userspace buffer overflow

[Greg Kroah-Hartman]

From: Vivien Didelot <vivien.dide...@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.dide...@gmail.com>
Reviewed-by: Michal Kubecek <mkube...@suse.cz>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/core/ethtool.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1402,13 +1402,16 @@ 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;