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

pppoe: drop PFC frames

RFC 2516 Section 7 states that Protocol Field Compression (PFC) is NOT
RECOMMENDED for PPPoE. In practice, pppd does not support negotiating
PFC for PPPoE sessions, and the current PPPoE driver assumes an
uncompressed (2-byte) protocol field. However, the generic PPP layer
function ppp_input() is not aware of the negotiation result, and still
accepts PFC frames.

If a peer with a broken implementation or an attacker sends a frame with
a compressed (1-byte) protocol field, the subsequent PPP payload is
shifted by one byte. This causes the network header to be 4-byte
misaligned, which may trigger unaligned access exceptions on some
architectures.

To reduce the attack surface, drop PPPoE PFC frames. Introduce
ppp_skb_is_compressed_proto() helper function to be used in both
ppp_generic.c and pppoe.c to avoid open-coding.

https://git.kernel.org/stable/c/0cab5d077dd1efd2bd1a47271acc35894f945b4f

https://git.kernel.org/stable/c/2b5c3c040d020e3ab3b9a8887031202d96843b1e

https://git.kernel.org/stable/c/49e41b60ccd1bdbe9e218420f716dd5f9a2f9c71

https://git.kernel.org/stable/c/8a5e840babc5c0fbd10c73728a13192347771ec6

https://git.kernel.org/stable/c/ba758fdf1399f310b30098b6faa3fd043de47dd2

https://git.kernel.org/stable/c/cb3beef35ab5e0c1afca9fd7648c6ae499786377

https://git.kernel.org/stable/c/cc1ff87bce1ccd38410ab10960f576dcd17db679

https://git.kernel.org/stable/c/fcca1df05322bb04e344dd1178b54b76a08eb7c3

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