On Mon, Jan 31, 2022 at 7:47 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > Matthew Wilcox reported that there is a missing mmap_lock in > file_files_note that could possibly lead to a user after free. > > Solve this by using the existing vma snapshot for consistency > and to avoid the need to take the mmap_lock anywhere in the > coredump code except for dump_vma_snapshot. > > Update the dump_vma_snapshot to capture vm_pgoff and vm_file > that are neeeded by fill_files_note. > > Add free_vma_snapshot to free the captured values of vm_file. > > Reported-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Link: https://lkml.kernel.org/r/20220131153740.2396974-1-willy@xxxxxxxxxxxxx > Cc: stable@xxxxxxxxxxxxxxx > Fixes: a07279c9a8cd ("binfmt_elf, binfmt_elf_fdpic: use a VMA list snapshot") > Fixes: 2aa362c49c31 ("coredump: extend core dump note section to contain file names of mapped files") > Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> [...] > +static int fill_files_note(struct memelfnote *note, struct coredump_params *cprm) > { > struct mm_struct *mm = current->mm; > - struct vm_area_struct *vma; > unsigned count, size, names_ofs, remaining, n; > user_long_t *data; > user_long_t *start_end_ofs; > char *name_base, *name_curpos; > + int i; > > /* *Estimated* file count and total data size needed */ > count = mm->map_count; This function is still looking at mm->map_count in two spots, please change those spots to also look at cprm->vma_count. In particular the second one looks like it can cause memory corruption if the map_count changed since we created the snapshot. [...] > +static void free_vma_snapshot(struct coredump_params *cprm) > +{ > + if (cprm->vma_meta) { > + int i; > + for (i = 0; i < cprm->vma_count; i++) { > + struct file *file = cprm->vma_meta[i].file; > + if (file) > + fput(file); > + } > + kvfree(cprm->vma_meta); > + cprm->vma_meta = NULL; (this NULL write is superfluous, but it also doesn't hurt) > + } > +}
