* Vlastimil Babka <vbabka@xxxxxxx> [220119 05:53]:
> On 12/1/21 15:30, Liam Howlett wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> >
> > I'm not sure if the VMA list can change under us, but dump_vma_snapshot()
> > is very careful to take the mmap_lock in write mode. We only need to
> > take it in read mode here as we do not care if the size of the stack
> > VMA changes underneath us.
> >
> > If it can be changed underneath us, this is a potential use-after-free
> > for a multithreaded process which is dumping core.
> >
> > Fixes: 2aa362c49c31 ("coredump: extend core dump note section to contain file names of mapped files")
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
>
> To be honest this feels out of place in this series. Send separately and CC
> Jann who AFAICS added dump_vma_snapshot()?
Thanks. I have moved the version Matthew sent out separately to the
start of my v5 set.
>
> > ---
> > fs/binfmt_elf.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index d41cca755ff9..5915518c8a1d 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1652,6 +1652,7 @@ static int fill_files_note(struct memelfnote *note)
> > name_base = name_curpos = ((char *)data) + names_ofs;
> > remaining = size - names_ofs;
> > count = 0;
> > + mmap_read_lock(mm);
> > for_each_vma(vmi, vma) {
> > struct file *file;
> > const char *filename;
> > @@ -1662,6 +1663,7 @@ static int fill_files_note(struct memelfnote *note)
> > filename = file_path(file, name_curpos, remaining);
> > if (IS_ERR(filename)) {
> > if (PTR_ERR(filename) == -ENAMETOOLONG) {
> > + mmap_read_unlock(mm);
> > kvfree(data);
> > size = size * 5 / 4;
> > goto alloc;
> > @@ -1681,6 +1683,7 @@ static int fill_files_note(struct memelfnote *note)
> > *start_end_ofs++ = vma->vm_pgoff;
> > count++;
> > }
> > + mmap_read_unlock(mm);
> >
> > /* Now we know exact count of files, can store it */
> > data[0] = count;
>
