Hello Stable Maintainers,

Longterm kernel 6.12.y backports commit:

- a18dfa9925b9ef6107ea3aa5814ca3c704d34a8a "ipv6: save dontfrag in cork"

but does not backport these related commits:

- 54580ccdd8a9c6821fd6f72171d435480867e4c3 "ipv6: remove leftover ip6 cookie initializer" - 096208592b09c2f5fc0c1a174694efa41c04209d "ipv6: replace ipcm6_init calls with ipcm6_init_sk"

This causes a regression when sending IPv6 UDP packets by preventing fragmentation and instead returning EMSGSIZE. I have attached a program which demonstrates the issue.

sendmsg() returns correctly (8192) on a working kernel, and returns -1 (EMSGSIZE) when the regression is present.

The regression is not present in the mainline kernel.

Applying the two missing commits to 6.12.y fixes the regression.

Cheers,

Brett