ethtool: Allow zero-length register dumps again

Some drivers (ab)use the ethtool_ops::get_regs operation to expose
only a hardware revision ID.  Commit
a77f5db361ed9953b5b749353ea2c7fed2bf8d93 ('ethtool: Allocate register
dump buffer with vmalloc()') had the side-effect of breaking these, as
vmalloc() returns a null pointer for size=0 whereas kmalloc() did not.

For backward-compatibility, allow zero-length dumps again.

Reported-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Cc: stable@kernel.org [2.6.37+]
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index b7c12a63d0ceb66166e8c2e4d3adc6ba1888d87a..6cdba5fc2beddf4e8b5c02ca3907a199bb09198c 100644 (file)
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -923,7 +923,7 @@ static int ethtool_get_regs(struct net_device *dev, char __user *useraddr)
                regs.len = reglen;
 
        regbuf = vzalloc(reglen);
-       if (!regbuf)
+       if (reglen && !regbuf)
                return -ENOMEM;
 
        ops->get_regs(dev, &regs, regbuf);
@@ -932,7 +932,7 @@ static int ethtool_get_regs(struct net_device *dev, char __user *useraddr)
        if (copy_to_user(useraddr, &regs, sizeof(regs)))
                goto out;
        useraddr += offsetof(struct ethtool_regs, data);
-       if (copy_to_user(useraddr, regbuf, regs.len))
+       if (regbuf && copy_to_user(useraddr, regbuf, regs.len))
                goto out;
        ret = 0;