On Tue, Oct 27, 2020 at 12:54 AM Sasha Levin <sashal@xxxxxxxxxx> wrote: > [ Upstream commit b2767d97f5ff758250cf28684aaa48bbfd34145f ] > > create_elf_tables() runs after setup_new_exec(), so other tasks can > already access our new mm and do things like process_madvise() on it. (At > the time I'm writing this commit, process_madvise() is not in mainline > yet, but has been in akpm's tree for some time.) > > While I believe that there are currently no APIs that would actually allow > another process to mess up our VMA tree (process_madvise() is limited to > MADV_COLD and MADV_PAGEOUT, and uring and userfaultfd cannot reach an mm > under which no syscalls have been executed yet), this seems like an > accident waiting to happen. > > Let's make sure that we always take the mmap lock around GUP paths as long > as another process might be able to see the mm. While this commit makes the kernel less prone to future accidents, and it is arguably fixing locking misbehavior, I don't think it belongs into stable trees? As far as I know, it is not fixing any bugs that can actually materialize in current or past kernels.
