CVE-2021-47224

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

net: ll_temac: Make sure to free skb when it is completely used

With the skb pointer piggy-backed on the TX BD, we have a simple and efficient way to free the skb buffer when the frame has been transmitted. But in order to avoid freeing the skb while there are still fragments from the skb in use, we need to piggy-back on the TX BD of the skb, not the first.

Without this, we are doing use-after-free on the DMA side, when the first BD of a multi TX BD packet is seen as completed in xmit_done, and the remaining BDs are still being processed.

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/019ab7d044d0ebf97e1236bb8935b7809be92358
• https://git.kernel.org/stable/c/6aa32217a9a446275440ee8724b1ecaf1838df47
• https://git.kernel.org/stable/c/6d120ab4dc39a543c6b63361e1d0541c382900a3
• https://git.kernel.org/stable/c/e8afe05bd359ebe12a61dbdc94c06c00ea3e8d4b
• https://git.kernel.org/stable/c/019ab7d044d0ebf97e1236bb8935b7809be92358
• https://git.kernel.org/stable/c/6aa32217a9a446275440ee8724b1ecaf1838df47
• https://git.kernel.org/stable/c/6d120ab4dc39a543c6b63361e1d0541c382900a3
• https://git.kernel.org/stable/c/e8afe05bd359ebe12a61dbdc94c06c00ea3e8d4b