[SRU][M][PATCH 0/1] CVE-2024-26803

[Bethany Jamison]

[Impact]

 In the Linux kernel, the following vulnerability has been resolved:

 net: veth: clear GRO when clearing XDP even when down

 veth sets NETIF_F_GRO automatically when XDP is enabled,
 because both features use the same NAPI machinery.

 The logic to clear NETIF_F_GRO sits in veth_disable_xdp() which
 is called both on ndo_stop and when XDP is turned off.
 To avoid the flag from being cleared when the device is brought
 down, the clearing is skipped when IFF_UP is not set.
 Bringing the device down should indeed not modify its features.

 Unfortunately, this means that clearing is also skipped when
 XDP is disabled _while_ the device is down. And there's nothing
 on the open path to bring the device features back into sync.
 IOW if user enables XDP, disables it and then brings the device
 up we'll end up with a stray GRO flag set but no NAPI instances.

 We don't depend on the GRO flag on the datapath, so the datapath
 won't crash. We will crash (or hang), however, next time features
 are sync'ed (either by user via ethtool or peer changing its config).
 The GRO flag will go away, and veth will try to disable the NAPIs.
 But the open path never created them since XDP was off, the GRO flag
 was a stray. If NAPI was initialized before we'll hang in napi_disable().
 If it never was we'll crash trying to stop uninitialized hrtimer.

 Move the GRO flag updates to the XDP enable / disable paths,
 instead of mixing them with the ndo_open / ndo_close paths.

[Fix]

Mantic:	Clean cherry-pick from linux-6.6.y
Jammy:	pending
Focal:	not-affected
Bionic: not-affected
Xenial:	not-affected
Trusty:	not-affected

[Test Case]

Compile and boot tested.

[Where problems could occur]

This fix affects those who use the veth (virtual ethernet) driver, an 
issue with this fix would be visable to the user via a system crash.

Jakub Kicinski (1):
  net: veth: clear GRO when clearing XDP even when down

 drivers/net/veth.c | 35 +++++++++++++++++------------------
 1 file changed, 17 insertions(+), 18 deletions(-)

-- 
2.34.1