media: mc: fix potential use-after-free in media_request_alloc()

media: mc: fix potential use-after-free in media_request_alloc()

Commit 6f504cbf108a ("media: convert media_request_alloc() to
FD_PREPARE()") moved the call to fd_install() (now hidden in
fd_publish()) before the snprintf(), making the later write to
potentially already freed memory, as userland is free to call
close() concurrently right after the call to fd_install() which
may end up in the request_fops.release() handler freeing 'req'.

Fixes: 6f504cbf108a ("media: convert media_request_alloc() to FD_PREPARE()")
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://patch.msgid.link/20251209210903.603958-1-minipli@grsecurity.net
Signed-off-by: Christian Brauner <brauner@kernel.org>