CVE-2023-53641

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

wifi: ath9k: hif_usb: fix memory leak of remain_skbs

hif_dev->remain_skb is allocated and used exclusively in ath9k_hif_usb_rx_stream(). It is implied that an allocated remain_skb is processed and subsequently freed (in error paths) only during the next call of ath9k_hif_usb_rx_stream().

So, if the urbs are deallocated between those two calls due to the device deinitialization or suspend, it is possible that ath9k_hif_usb_rx_stream() is not called next time and the allocated remain_skb is leaked. Our local Syzkaller instance was able to trigger that.

remain_skb makes sense when receiving two consecutive urbs which are logically linked together, i.e. a specific data field from the first skb indicates a cached skb to be allocated, memcpyd with some data and subsequently processed in the next call to ath9k_hif_usb_rx_stream(). Urbs deallocation supposedly makes that link irrelevant so we need to free the cached skb in those cases.

Fix the leak by introducing a function to explicitly free remain_skb (if it is not NULL) when the rx urbs have been deallocated. remain_skb is NULL when it has not been allocated at all (hif_dev struct is kzalloced) or when it has been processed in next call to ath9k_hif_usb_rx_stream().

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Weakness

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/320d760a35273aa815d58b57e4fd9ba5279a3489
• https://git.kernel.org/stable/c/59073060fe0950c6ecbe12bdc06469dcac62128d
• https://git.kernel.org/stable/c/6719e3797ec52cd144c8a5ba8aaab36674800585
• https://git.kernel.org/stable/c/7654cc03eb699297130b693ec34e25f77b17c947
• https://git.kernel.org/stable/c/8f02d538878c9b1501f624595eb22ee4e5e0ff84
• https://git.kernel.org/stable/c/9b9356a3014123f0ce4b50d9278c1265173150ab
• https://git.kernel.org/stable/c/d9899318660791141ea6002fda5577b2c5d7386e
• https://git.kernel.org/stable/c/f0931fc8f4b6847c72e170d2326861c0a081d680