CVE-2022-49669

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

mptcp: fix race on unaccepted mptcp sockets

When the listener socket owning the relevant request is closed, it frees the unaccepted subflows and that causes later deletion of the paired MPTCP sockets.

The mptcp sockets worker can run in the time interval between such delete operations. When that happens, any access to msk->first will cause an UaF access, as the subflow cleanup did not cleared such field in the mptcp socket.

Address the issue explicitly traversing the listener socket accept queue at close time and performing the needed cleanup on the pending msk.

Note that the locking is a bit tricky, as we need to acquire the msk socket lock, while still owning the subflow socket one.

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/6aeed9045071f2252ff4e98fc13d1e304f33e5b0
• https://git.kernel.org/stable/c/a8a3e95c74e48c2c9b07b81fafda9122993f2e12