CVE-2024-45016

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

netem: fix return value if duplicate enqueue fails

There is a bug in netem_enqueue() introduced by commit 5845f706388a (net: netem: fix skb length BUG_ON in __skb_to_sgvec) that can lead to a use-after-free.

This commit made netem_enqueue() always return NET_XMIT_SUCCESS when a packet is duplicated, which can cause the parent qdiscs q.qlen to be mistakenly incremented. When this happens qlen_notify() may be skipped on the parent during destruction, leaving a dangling pointer for some classful qdiscs like DRR.

There are two ways for the bug happen:

• If the duplicated packet is dropped by rootq->enqueue() and then the original packet is also dropped.
• If rootq->enqueue() sends the duplicated packet to a different qdisc and the original packet is dropped.

In both cases NET_XMIT_SUCCESS is returned even though no packets are enqueued at the netem qdisc.

The fix is to defer the enqueue of the duplicate packet until after the original packet has been guaranteed to return NET_XMIT_SUCCESS.

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/0486d31dd8198e22b63a4730244b38fffce6d469
• https://git.kernel.org/stable/c/52d99a69f3d556c6426048c9d481b912205919d8
• https://git.kernel.org/stable/c/577d6c0619467fe90f7e8e57e45cb5bd9d936014
• https://git.kernel.org/stable/c/759e3e8c4a6a6b4e52ebc4547123a457f0ce90d4
• https://git.kernel.org/stable/c/c07ff8592d57ed258afee5a5e04991a48dbaf382
• https://git.kernel.org/stable/c/c414000da1c2ea1ba9a5e5bb1a4ba774e51e202d
• https://git.kernel.org/stable/c/e5bb2988a310667abed66c7d3ffa28880cf0f883