On Fri, Sep 18, 2015 at 09:54:44AM +0200, Christian Borntraeger wrote:
> To avoid overwriting the upper bits of the flags, commit
> 39ec7de7092b ("macvtap: fix uninitialized access on
> TUNSETIFF") changed the variable u from unsigned int to
> unsigned short and added some ORing logic for the flags.
> This introduced at least one regression:
> - TUNSETSNDBUF supports int as its size and also uses the now
> short u as buffer - this breaks any sendbuf size > 64k
>
> Let's change u back to unsigned int, keep the ORing and
> handle the overwrite issue with casts and masking.
>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Reported-by: Mark A. Peloquin
> Bisected-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> Fixes: 39ec7de7092b ("macvtap: fix uninitialized access on TUNSETIFF")
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> drivers/net/macvtap.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index edd7734..c33fe41 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -1060,7 +1060,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
> void __user *argp = (void __user *)arg;
> struct ifreq __user *ifr = argp;
> unsigned int __user *up = argp;
> - unsigned short u;
> + unsigned int u;
> int __user *sp = argp;
> struct sockaddr sa;
> int s;
> @@ -1076,7 +1076,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
> if ((u & ~MACVTAP_FEATURES) != (IFF_NO_PI | IFF_TAP))
> ret = -EINVAL;
> else
> - q->flags = (q->flags & ~MACVTAP_FEATURES) | u;
> + q->flags = (q->flags & ~MACVTAP_FEATURES) | (short) u;
>
> return ret;
>
> @@ -1089,9 +1089,8 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
> }
>
> ret = 0;
> - u = q->flags;
> if (copy_to_user(&ifr->ifr_name, vlan->dev->name, IFNAMSIZ) ||
> - put_user(u, &ifr->ifr_flags))
> + put_user((short) q->flags, &ifr->ifr_flags))
> ret = -EFAULT;
> macvtap_put_vlan(vlan);
> rtnl_unlock();
I agree it's a bug, but I don't think it's reasonable to
read 32 bit from the flags field.
I'll send a patch shortly.
> --
> 2.3.0
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