Re: [PATCH bpf-next v2 1/3] bpf/verifier: Fix potential memory leak in array reallocation

[Daniel Borkmann]

[ +Lorenz ]

On 10/31/22 9:16 PM, Bill Wendling wrote:
> On Fri, Oct 28, 2022 at 7:55 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > If an error (NULL) is returned by krealloc(), callers of realloc_array()
> > were setting their allocation pointers to NULL, but on error krealloc()
> > does not touch the original allocation. This would result in a memory
> > resource leak. Instead, free the old allocation on the error handling
> > path.
> >
> > Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > Cc: John Fastabend <john.fastabend@xxxxxxxxx>
> > Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
> > Cc: Song Liu <song@xxxxxxxxxx>
> > Cc: Yonghong Song <yhs@xxxxxx>
> > Cc: KP Singh <kpsingh@xxxxxxxxxx>
> > Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > Cc: Hao Luo <haoluo@xxxxxxxxxx>
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Cc: bpf@xxxxxxxxxxxxxxx
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> Reviewed-by: Bill Wendling <morbo@xxxxxxxxxx>
>
> > ---
> >   kernel/bpf/verifier.c | 9 +++++++--
> >   1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 014ee0953dbd..eb8c34db74c7 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -1027,12 +1027,17 @@ static void *copy_array(void *dst, const void *src, size_t n, size_t size, gfp_t
> >    */
> >   static void *realloc_array(void *arr, size_t old_n, size_t new_n, size_t size)
> >   {
> > +       void *new_arr;
> > +
> >          if (!new_n || old_n == new_n)
> >                  goto out;
> >
> > -       arr = krealloc_array(arr, new_n, size, GFP_KERNEL);
> > -       if (!arr)
> > +       new_arr = krealloc_array(arr, new_n, size, GFP_KERNEL);
> > +       if (!new_arr) {
> > +               kfree(arr);
> >                  return NULL;
> > +       }
> > +       arr = new_arr;

Fyi, I took this fix into bpf tree and improved commit log a bit with the
one from Zhengchao [0] given yours came in first. Fixes tag would have been
nice, I added the c69431aab67a to the commit message while applying.

  [0] https://patchwork.kernel.org/project/netdevbpf/patch/20221031070812.339883-1-shaozhengchao@xxxxxxxxxx/

> >          if (new_n > old_n)
> >                  memset(arr + old_n * size, 0, (new_n - old_n) * size);
> > --
> > 2.34.1