From b2767d97f5ff758250cf28684aaa48bbfd34145f Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Sat, 17 Oct 2020 16:14:15 -0700 Subject: binfmt_elf: take the mmap lock around find_extend_vma() 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. (Yes, this diff looks suspicious because we drop the lock before doing anything with `vma`, but that's because we actually don't do anything with it apart from the NULL check.) Signed-off-by: Jann Horn Signed-off-by: Andrew Morton Acked-by: Michel Lespinasse Cc: "Eric W . Biederman" Cc: Jason Gunthorpe Cc: John Hubbard Cc: Mauro Carvalho Chehab Cc: Sakari Ailus Link: https://lkml.kernel.org/r/CAG48ez1-PBCdv3y8pn-Ty-b+FmBSLwDuVKFSt8h7wARLy0dF-Q@mail.gmail.com Signed-off-by: Linus Torvalds --- fs/binfmt_elf.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index e7e9d0cde51a..b6b3d052ca86 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -310,7 +310,10 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec, * Grow the stack manually; some architectures have a limit on how * far ahead a user-space access may be in order to grow the stack. */ + if (mmap_read_lock_killable(mm)) + return -EINTR; vma = find_extend_vma(mm, bprm->p); + mmap_read_unlock(mm); if (!vma) return -EFAULT; -- cgit v1.2.3