Re: [PATCH bpf-next v3 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

On Tue, May 17, 2022 at 09:36:15AM +0200, Eugene Syromiatnikov wrote:

Check that size would not overflow before calculation (and return -EOVERFLOW if it will), to prevent potential out-of-bounds write with the following copy_from_user. Use kvmalloc_array in copy_user_syms to prevent out-of-bounds write into syms (and especially buf) as well.

Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link") Cc: stable@vger.kernel.org # 5.18 Signed-off-by: Eugene Syromiatnikov esyr@redhat.com

Acked-by: Jiri Olsa jolsa@kernel.org

thanks, jirka

---

kernel/trace/bpf_trace.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 7141ca8..9c041be 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2261,11 +2261,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 int err = -ENOMEM; unsigned int i;

• syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);

• syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL); if (!syms) goto error;

• buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);

• buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL); if (!buf) goto error;

@@ -2461,7 +2461,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr if (!cnt) return -EINVAL;

• size = cnt * sizeof(*addrs);

• if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))

• return -EOVERFLOW;
  

  addrs = kvmalloc(size, GFP_KERNEL); if (!addrs) return -ENOMEM;

-- 2.1.4