From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> commit 390031c942116d4733310f0684beb8db19885fe6 upstream. 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") Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/binfmt_elf.c | 24 ++++++++++++------------ fs/coredump.c | 22 +++++++++++++++++++++- include/linux/coredump.h | 2 ++ 3 files changed, 35 insertions(+), 13 deletions(-) --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1642,17 +1642,16 @@ static void fill_siginfo_note(struct mem * long file_ofs * followed by COUNT filenames in ASCII: "FILE1" NUL "FILE2" NUL... */ -static int fill_files_note(struct memelfnote *note) +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; + count = cprm->vma_count; if (count > UINT_MAX / 64) return -EINVAL; size = count * 64; @@ -1674,11 +1673,12 @@ static int fill_files_note(struct memelf name_base = name_curpos = ((char *)data) + names_ofs; remaining = size - names_ofs; count = 0; - for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) { + for (i = 0; i < cprm->vma_count; i++) { + struct core_vma_metadata *m = &cprm->vma_meta[i]; struct file *file; const char *filename; - file = vma->vm_file; + file = m->file; if (!file) continue; filename = file_path(file, name_curpos, remaining); @@ -1698,9 +1698,9 @@ static int fill_files_note(struct memelf memmove(name_curpos, filename, n); name_curpos += n; - *start_end_ofs++ = vma->vm_start; - *start_end_ofs++ = vma->vm_end; - *start_end_ofs++ = vma->vm_pgoff; + *start_end_ofs++ = m->start; + *start_end_ofs++ = m->end; + *start_end_ofs++ = m->pgoff; count++; } @@ -1711,7 +1711,7 @@ static int fill_files_note(struct memelf * Count usually is less than mm->map_count, * we need to move filenames down. */ - n = mm->map_count - count; + n = cprm->vma_count - count; if (n != 0) { unsigned shift_bytes = n * 3 * sizeof(data[0]); memmove(name_base - shift_bytes, name_base, @@ -1910,7 +1910,7 @@ static int fill_note_info(struct elfhdr fill_auxv_note(&info->auxv, current->mm); info->size += notesize(&info->auxv); - if (fill_files_note(&info->files) == 0) + if (fill_files_note(&info->files, cprm) == 0) info->size += notesize(&info->files); return 1; @@ -2099,7 +2099,7 @@ static int fill_note_info(struct elfhdr fill_auxv_note(info->notes + 3, current->mm); info->numnote = 4; - if (fill_files_note(info->notes + info->numnote) == 0) { + if (fill_files_note(info->notes + info->numnote, cprm) == 0) { info->notes_files = info->notes + info->numnote; info->numnote++; } --- a/fs/coredump.c +++ b/fs/coredump.c @@ -55,6 +55,7 @@ #include <trace/events/sched.h> static bool dump_vma_snapshot(struct coredump_params *cprm); +static void free_vma_snapshot(struct coredump_params *cprm); static int core_uses_pid; static unsigned int core_pipe_limit; @@ -765,7 +766,7 @@ void do_coredump(const kernel_siginfo_t dump_emit(&cprm, "", 1); } file_end_write(cprm.file); - kvfree(cprm.vma_meta); + free_vma_snapshot(&cprm); } if (ispipe && core_pipe_limit) wait_for_dump_helpers(cprm.file); @@ -1099,6 +1100,20 @@ static struct vm_area_struct *next_vma(s return gate_vma; } +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; + } +} + /* * Under the mmap_lock, take a snapshot of relevant information about the task's * VMAs. @@ -1135,6 +1150,11 @@ static bool dump_vma_snapshot(struct cor m->end = vma->vm_end; m->flags = vma->vm_flags; m->dump_size = vma_dump_size(vma, cprm->mm_flags); + m->pgoff = vma->vm_pgoff; + + m->file = vma->vm_file; + if (m->file) + get_file(m->file); } mmap_write_unlock(mm); --- a/include/linux/coredump.h +++ b/include/linux/coredump.h @@ -12,6 +12,8 @@ struct core_vma_metadata { unsigned long start, end; unsigned long flags; unsigned long dump_size; + unsigned long pgoff; + struct file *file; }; /*
