sch/netem: fix use after free in netem_dequeue

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sch/netem: fix use after free in netem_dequeue If netem_dequeue() enqueues packet to inner qdisc and that qdisc returns __NET_XMIT_STOLEN. The packet is dropped but qdisc_tree_reduce_backlog() is not called to update the parent's q.qlen, leading to the similar use-after-free as Commit e04991a48dbaf382 ("netem: fix return value if duplicate enqueue fails") Commands to trigger KASAN UaF: ip link add type dummy ip link set lo up ip link set dummy0 up tc qdisc add dev lo parent root handle 1: drr tc filter add dev lo parent 1: basic classid 1:1 tc class add dev lo classid 1:1 drr tc qdisc add dev lo parent 1:1 handle 2: netem tc qdisc add dev lo parent 2: handle 3: drr tc filter add dev lo parent 3: basic classid 3:1 action mirred egress redirect dev dummy0 tc class add dev lo classid 3:1 drr ping -c1 -W0.01 localhost # Trigger bug tc class del dev lo classid 1:1 tc class add dev lo classid 1:1 drr ping -c1 -W0.01 localhost # UaF

References

• https://git.kernel.org/stable/c/f0bddb4de043399f16d1969dad5ee5b984a64e7b
• https://git.kernel.org/stable/c/295ad5afd9efc5f67b86c64fce28fb94e26dc4c9
• https://git.kernel.org/stable/c/98c75d76187944296068d685dfd8a1e9fd8c4fdc
• https://git.kernel.org/stable/c/14f91ab8d391f249b845916820a56f42cf747241
• https://git.kernel.org/stable/c/db2c235682913a63054e741fe4e19645fdf2d68e
• https://git.kernel.org/stable/c/dde33a9d0b80aae0c69594d1f462515d7ff1cb3d
• https://git.kernel.org/stable/c/32008ab989ddcff1a485fa2b4906234c25dc5cd6
• https://git.kernel.org/stable/c/3b3a2a9c6349e25a025d2330f479bc33a6ccb54a