CVE-2024-53057

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

net/sched: stop qdisc_tree_reduce_backlog on TC_H_ROOT

In qdisc_tree_reduce_backlog, Qdiscs with major handle ffff: are assumed to be either root or ingress. This assumption is bogus since its valid to create egress qdiscs with major handle ffff: Budimir Markovic found that for qdiscs like DRR that maintain an active class list, it will cause a UAF with a dangling class pointer.

In 066a3b5b2346, the concern was to avoid iterating over the ingress qdisc since its parent is itself. The proper fix is to stop when parent TC_H_ROOT is reached because the only way to retrieve ingress is when a hierarchy which does not contain a ffff: major handle call into qdisc_lookup with TC_H_MAJ(TC_H_ROOT).

In the scenario where major ffff: is an egress qdisc in any of the tree levels, the updates will also propagate to TC_H_ROOT, which then the iteration must stop.

net/sched/sch_api.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

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/05df1b1dff8f197f1c275b57ccb2ca33021df552
• https://git.kernel.org/stable/c/2e95c4384438adeaa772caa560244b1a2efef816
• https://git.kernel.org/stable/c/580b3189c1972aff0f993837567d36392e9d981b
• https://git.kernel.org/stable/c/597cf9748c3477bf61bc35f0634129f56764ad24
• https://git.kernel.org/stable/c/9995909615c3431a5304c1210face5f268d24dba
• https://git.kernel.org/stable/c/ce691c814bc7a3c30c220ffb5b7422715458fd9b
• https://git.kernel.org/stable/c/dbe778b08b5101df9e89bc06e0a3a7ecd2f4ef20
• https://git.kernel.org/stable/c/e7f9a6f97eb067599a74f3bcb6761976b0ed303e