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>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index b7c12a63d0ce..6cdba5fc2bed 100644
--- 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;