wifi: ath9k: avoid uninit memory read in ath9k_htc_rx_msg()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: wifi: ath9k: avoid uninit memory read in ath9k_htc_rx_msg() syzbot is reporting uninit value at ath9k_htc_rx_msg() [1], for ioctl(USB_RAW_IOCTL_EP_WRITE) can call ath9k_hif_usb_rx_stream() with pkt_len = 0 but ath9k_hif_usb_rx_stream() uses __dev_alloc_skb(pkt_len + 32, GFP_ATOMIC) based on an assumption that pkt_len is valid. As a result, ath9k_hif_usb_rx_stream() allocates skb with uninitialized memory and ath9k_htc_rx_msg() is reading from uninitialized memory. Since bytes accessed by ath9k_htc_rx_msg() is not known until ath9k_htc_rx_msg() is called, it would be difficult to check minimal valid pkt_len at "if (pkt_len > 2 * MAX_RX_BUF_SIZE) {" line in ath9k_hif_usb_rx_stream(). We have two choices. One is to workaround by adding __GFP_ZERO so that ath9k_htc_rx_msg() sees 0 if pkt_len is invalid. The other is to let ath9k_htc_rx_msg() validate pkt_len before accessing. This patch chose the latter. Note that I'm not sure threshold condition is correct, for I can't find details on possible packet length used by this protocol.

References

• https://git.kernel.org/stable/c/f3d2a3b7e290d0bdbddfcee5a6c3d922e2b7e02a
• https://git.kernel.org/stable/c/84242f15f911f34aec9b22f99d1e9bff19723dbe
• https://git.kernel.org/stable/c/2c485f4f2a64258acc5228e78ffb828c68d9e770
• https://git.kernel.org/stable/c/9661724f6206bd606ecf13acada676a9975d230b
• https://git.kernel.org/stable/c/b1b4144508adfc585e43856b31baaf9008a3beb4
• https://git.kernel.org/stable/c/0d2649b288b7b9484e3d4380c0d6c4720a17e473
• https://git.kernel.org/stable/c/4891a50f5ed8bfcb8f2a4b816b0676f398687783
• https://git.kernel.org/stable/c/b383e8abed41cc6ff1a3b34de75df9397fa4878c