CVE-2024-46800

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 parents 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

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

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