net: tap: fix NULL dereference when passing both fd and vhostfds to tap

This is because vhostfdname were passed as NULL to net_init_tap_one() when
vhostfd were not specified, but net_init_tap_one() will still pass it to
monitor_handle_fd_param() when tap->has_vhostfds is true. Since file descriptor
(fd, vhostfd) and file descriptor set (fds, vhostfds) were not compatible, so
this patch forbids passing them to tap in the same time.

This solve the segfault when passing the command line like:
./qemu-system-x86_64 -netdev tap,fd=2,vhost=on,vhostfds=baz,id=xyz

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <shajnocz@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 net/tap.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

comments below

On 06/03/13 11:04, Jason Wang wrote:
> This is because vhostfdname were passed as NULL to net_init_tap_one() when
> vhostfd were not specified, but net_init_tap_one() will still pass it to
> monitor_handle_fd_param() when tap->has_vhostfds is true. Since file descriptor
> (fd, vhostfd) and file descriptor set (fds, vhostfds) were not compatible, so
> this patch forbids passing them to tap in the same time.
> 
> This solve the segfault when passing the command line like:
> ./qemu-system-x86_64 -netdev tap,fd=2,vhost=on,vhostfds=baz,id=xyz
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Stefan Hajnoczi <shajnocz@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  net/tap.c |   10 ++++++----
>  1 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/net/tap.c b/net/tap.c
> index e0b7a2a..477505f 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -698,9 +698,10 @@ int net_init_tap(const NetClientOptions *opts, const char *name,
>      if (tap->has_fd) {
>          if (tap->has_ifname || tap->has_script || tap->has_downscript ||
>              tap->has_vnet_hdr || tap->has_helper || tap->has_queues ||
> -            tap->has_fds) {
> +            tap->has_fds || tap->has_vhostfds) {
>              error_report("ifname=, script=, downscript=, vnet_hdr=, "
> -                         "helper=, queues=, and fds= are invalid with fd=");
> +                         "helper=, queues=, fds=, and vhostfds= "
> +                         "are invalid with fd=");
>              return -1;
>          }
>  

This seems OK, since

has_fd                   precludes    has_fds
- optional: has_vhostfd               - optional: has_vhostfds

> @@ -725,9 +726,10 @@ int net_init_tap(const NetClientOptions *opts, const char *name,
>  
>          if (tap->has_ifname || tap->has_script || tap->has_downscript ||
>              tap->has_vnet_hdr || tap->has_helper || tap->has_queues ||
> -            tap->has_fd) {
> +            tap->has_fd || tap->has_vhostfd) {
>              error_report("ifname=, script=, downscript=, vnet_hdr=, "
> -                         "helper=, queues=, and fd= are invalid with fds=");
> +                         "helper=, queues=, fd=, and vhostfd= "
> +                         "are invalid with fds=");
>              return -1;
>          }
>  
> 

I think this us OK too (implementing the above exclusion from the other
side), but in the second hunk "tap->has_fd" can never be true actually.
I think relying on that in both the condition and the error message here
would simplify them.


Finally, I think the "has_helper", and the outermost "else" branch
should both be updated as well, for consistency with hunk #1 here. These
branches use "vhostfdname" too. In these branches,
- both "has_fd" and "has_fds" are false (should simplify check & errmsg),
- "has_vhostfds" should be rejected.

Thanks
Laszlo

On 06/03/2013 06:48 PM, Laszlo Ersek wrote:
> comments below
>
> On 06/03/13 11:04, Jason Wang wrote:
>> This is because vhostfdname were passed as NULL to net_init_tap_one() when
>> vhostfd were not specified, but net_init_tap_one() will still pass it to
>> monitor_handle_fd_param() when tap->has_vhostfds is true. Since file descriptor
>> (fd, vhostfd) and file descriptor set (fds, vhostfds) were not compatible, so
>> this patch forbids passing them to tap in the same time.
>>
>> This solve the segfault when passing the command line like:
>> ./qemu-system-x86_64 -netdev tap,fd=2,vhost=on,vhostfds=baz,id=xyz
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Stefan Hajnoczi <shajnocz@redhat.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: qemu-stable@nongnu.org
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>  net/tap.c |   10 ++++++----
>>  1 files changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/net/tap.c b/net/tap.c
>> index e0b7a2a..477505f 100644
>> --- a/net/tap.c
>> +++ b/net/tap.c
>> @@ -698,9 +698,10 @@ int net_init_tap(const NetClientOptions *opts, const char *name,
>>      if (tap->has_fd) {
>>          if (tap->has_ifname || tap->has_script || tap->has_downscript ||
>>              tap->has_vnet_hdr || tap->has_helper || tap->has_queues ||
>> -            tap->has_fds) {
>> +            tap->has_fds || tap->has_vhostfds) {
>>              error_report("ifname=, script=, downscript=, vnet_hdr=, "
>> -                         "helper=, queues=, and fds= are invalid with fd=");
>> +                         "helper=, queues=, fds=, and vhostfds= "
>> +                         "are invalid with fd=");
>>              return -1;
>>          }
>>  
> This seems OK, since
>
> has_fd                   precludes    has_fds
> - optional: has_vhostfd               - optional: has_vhostfds
>
>> @@ -725,9 +726,10 @@ int net_init_tap(const NetClientOptions *opts, const char *name,
>>  
>>          if (tap->has_ifname || tap->has_script || tap->has_downscript ||
>>              tap->has_vnet_hdr || tap->has_helper || tap->has_queues ||
>> -            tap->has_fd) {
>> +            tap->has_fd || tap->has_vhostfd) {
>>              error_report("ifname=, script=, downscript=, vnet_hdr=, "
>> -                         "helper=, queues=, and fd= are invalid with fds=");
>> +                         "helper=, queues=, fd=, and vhostfd= "
>> +                         "are invalid with fds=");
>>              return -1;
>>          }
>>  
>>
> I think this us OK too (implementing the above exclusion from the other
> side), but in the second hunk "tap->has_fd" can never be true actually.
> I think relying on that in both the condition and the error message here
> would simplify them.

Ture
>
>
> Finally, I think the "has_helper", and the outermost "else" branch
> should both be updated as well, for consistency with hunk #1 here. These
> branches use "vhostfdname" too. In these branches,
> - both "has_fd" and "has_fds" are false (should simplify check & errmsg),
> - "has_vhostfds" should be rejected.

Sure will send v2.

Thanks
> Thanks
> Laszlo
>