These are missing throughout ucma, it harmlessly copies garbage from
userspace, but in this new code which uses min to compute the copy length
it can result in uninitialized stack memory. Check for minimum length at
the very start.

  BUG: KMSAN: uninit-value in ucma_connect+0x2aa/0xab0 drivers/infiniband/core/ucma.c:1091
  CPU: 0 PID: 8457 Comm: syz-executor069 Not tainted 5.8.0-rc5-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  Call Trace:
   __dump_stack lib/dump_stack.c:77 [inline]
   dump_stack+0x1df/0x240 lib/dump_stack.c:118
   kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
   __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
   ucma_connect+0x2aa/0xab0 drivers/infiniband/core/ucma.c:1091
   ucma_write+0x5c5/0x630 drivers/infiniband/core/ucma.c:1764
   do_loop_readv_writev fs/read_write.c:737 [inline]
   do_iter_write+0x710/0xdc0 fs/read_write.c:1020
   vfs_writev fs/read_write.c:1091 [inline]
   do_writev+0x42d/0x8f0 fs/read_write.c:1134
   __do_sys_writev fs/read_write.c:1207 [inline]
   __se_sys_writev+0x9b/0xb0 fs/read_write.c:1204
   __x64_sys_writev+0x4a/0x70 fs/read_write.c:1204
   do_syscall_64+0xb0/0x150 arch/x86/entry/common.c:386
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 34e2ab57 ("RDMA/ucma: Extend ucma_connect to receive ECE parameters")
Fixes: 0cb15372 ("RDMA/cma: Connect ECE to rdma_accept")
Link: https://lore.kernel.org/r/0-v1-d5b86dab17dc+28c25-ucma_syz_min_jgg@nvidia.com
Reported-by: syzbot+086ab5ca9eafd2379aa6@syzkaller.appspotmail.com
Reported-by: syzbot+7446526858b83c8828b2@syzkaller.appspotmail.com
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>