Description: af_unix: Fix null-ptr-deref in unix_stream_sendpage().
References:
 https://kernel.dance/790c2f9d15b594350ae9bca7b236f2b1859de02c
Notes:
 carnil> Consider the 57d44a354a43 ("unix: Convert
 carnil> unix_stream_sendpage() to use MSG_SPLICE_PAGES") commit, part
 carnil> of the sendpage refactoring the fixing commit.
 carnil> For 6.4.y fixed in 6.4.12.
Bugs:
upstream: released (6.5-rc1) [57d44a354a43edba4ef9963327d4657d12edbfbc]
6.1-upstream-stable: released (6.1.47) [790c2f9d15b594350ae9bca7b236f2b1859de02c]
5.10-upstream-stable: released (5.10.192) [c080cee930303124624fe64fc504f66c815ee6b9]
4.19-upstream-stable: released (4.19.293) [bd6303bef49970ac7f9278a94473b587e19d1ee2]
sid: released (6.4.13-1)
6.1-bookworm-security: released (6.1.52-1)
5.10-bullseye-security: released (5.10.197-1)
4.19-buster-security: released (4.19.304-1)