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authorDaniel P. Berrange <berrange@redhat.com>2020-07-07 20:45:15 +0200
committerJason Wang <jasowang@redhat.com>2020-07-15 21:00:13 +0800
commite7b347d0bf640adb1c998d317eaf44d2d7cbd973 (patch)
tree6b5cddeececae40a6e56209bdb4d23d80558a3ca /net/tap.c
parent894022e616016fe81745753f14adfbd680a1c7ee (diff)
net: detect errors from probing vnet hdr flag for TAP devices
When QEMU sets up a tap based network device backend, it mostly ignores errors reported from various ioctl() calls it makes, assuming the TAP file descriptor is valid. This assumption can easily be violated when the user is passing in a pre-opened file descriptor. At best, the ioctls may fail with a -EBADF, but if the user passes in a bogus FD number that happens to clash with a FD number that QEMU has opened internally for another reason, a wide variety of errnos may result, as the TUNGETIFF ioctl number may map to a completely different command on a different type of file. By ignoring all these errors, QEMU sets up a zombie network backend that will never pass any data. Even worse, when QEMU shuts down, or that network backend is hot-removed, it will close this bogus file descriptor, which could belong to another QEMU device backend. There's no obvious guaranteed reliable way to detect that a FD genuinely is a TAP device, as opposed to a UNIX socket, or pipe, or something else. Checking the errno from probing vnet hdr flag though, does catch the big common cases. ie calling TUNGETIFF will return EBADF for an invalid FD, and ENOTTY when FD is a UNIX socket, or pipe which catches accidental collisions with FDs used for stdio, or monitor socket. Previously the example below where bogus fd 9 collides with the FD used for the chardev saw: $ ./x86_64-softmmu/qemu-system-x86_64 -netdev tap,id=hostnet0,fd=9 \ -chardev socket,id=charchannel0,path=/tmp/qga,server,nowait \ -monitor stdio -vnc :0 qemu-system-x86_64: -netdev tap,id=hostnet0,fd=9: TUNGETIFF ioctl() failed: Inappropriate ioctl for device TUNSETOFFLOAD ioctl() failed: Bad address QEMU 2.9.1 monitor - type 'help' for more information (qemu) Warning: netdev hostnet0 has no peer which gives a running QEMU with a zombie network backend. With this change applied we get an error message and QEMU immediately exits before carrying on and making a bigger disaster: $ ./x86_64-softmmu/qemu-system-x86_64 -netdev tap,id=hostnet0,fd=9 \ -chardev socket,id=charchannel0,path=/tmp/qga,server,nowait \ -monitor stdio -vnc :0 qemu-system-x86_64: -netdev tap,id=hostnet0,vhost=on,fd=9: Unable to query TUNGETIFF on FD 9: Inappropriate ioctl for device Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Message-id: 20171027085548.3472-1-berrange@redhat.com [lv: to simplify, don't check on EINVAL with TUNGETIFF as it exists since v2.6.27] Signed-off-by: Laurent Vivier <lvivier@redhat.com> Signed-off-by: Jason Wang <jasowang@redhat.com>
Diffstat (limited to 'net/tap.c')
-rw-r--r--net/tap.c25
1 files changed, 20 insertions, 5 deletions
diff --git a/net/tap.c b/net/tap.c
index 32e4813dbc..14dc904fca 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -598,7 +598,11 @@ int net_init_bridge(const Netdev *netdev, const char *name,
}
qemu_set_nonblock(fd);
- vnet_hdr = tap_probe_vnet_hdr(fd);
+ vnet_hdr = tap_probe_vnet_hdr(fd, errp);
+ if (vnet_hdr < 0) {
+ close(fd);
+ return -1;
+ }
s = net_tap_fd_init(peer, "bridge", name, fd, vnet_hdr);
snprintf(s->nc.info_str, sizeof(s->nc.info_str), "helper=%s,br=%s", helper,
@@ -810,7 +814,11 @@ int net_init_tap(const Netdev *netdev, const char *name,
return -1;
}
- vnet_hdr = tap_probe_vnet_hdr(fd);
+ vnet_hdr = tap_probe_vnet_hdr(fd, errp);
+ if (vnet_hdr < 0) {
+ close(fd);
+ return -1;
+ }
net_init_tap_one(tap, peer, "tap", name, NULL,
script, downscript,
@@ -862,8 +870,11 @@ int net_init_tap(const Netdev *netdev, const char *name,
}
if (i == 0) {
- vnet_hdr = tap_probe_vnet_hdr(fd);
- } else if (vnet_hdr != tap_probe_vnet_hdr(fd)) {
+ vnet_hdr = tap_probe_vnet_hdr(fd, errp);
+ if (vnet_hdr < 0) {
+ goto free_fail;
+ }
+ } else if (vnet_hdr != tap_probe_vnet_hdr(fd, NULL)) {
error_setg(errp,
"vnet_hdr not consistent across given tap fds");
ret = -1;
@@ -908,7 +919,11 @@ free_fail:
}
qemu_set_nonblock(fd);
- vnet_hdr = tap_probe_vnet_hdr(fd);
+ vnet_hdr = tap_probe_vnet_hdr(fd, errp);
+ if (vnet_hdr < 0) {
+ close(fd);
+ return -1;
+ }
net_init_tap_one(tap, peer, "bridge", name, ifname,
script, downscript, vhostfdname,