[029/102] ethtool: Allow zero-length register dumps again

[Greg KH]

3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>

commit 67ae7cf1eeda777f79259c4c6cb17a0bd28dee71 upstream.

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@xxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 net/core/ethtool.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1227,7 +1227,7 @@ static int ethtool_get_regs(struct net_d
 		regs.len = reglen;
 
 	regbuf = vzalloc(reglen);
-	if (!regbuf)
+	if (reglen && !regbuf)
 		return -ENOMEM;
 
 	ops->get_regs(dev, &regs, regbuf);
@@ -1236,7 +1236,7 @@ static int ethtool_get_regs(struct net_d
 	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;
 


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