On Thu, May 19, 2022 at 7:37 AM Eugene Syromiatnikov esyr@redhat.com wrote:
On Wed, May 18, 2022 at 04:30:14PM -0700, Andrii Nakryiko wrote:
On Tue, May 17, 2022 at 12:36 AM Eugene Syromiatnikov esyr@redhat.com 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
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);any good reason not to use kvmalloc_array() here as well and delegate overflow to it. And then use long size (as expected by copy_from_user anyway) everywhere?
Just to avoid double calculation of size, otherwise I don't have any significant prefernce, other than -EOVERFLOW would not be reported separately (not sure if this a good or a bad thing), and that it would be a bit more cumbersome to incorporate the Yonghong's suggestion[1] about the INT_MAX check.
I think it's totally fine to return ENOMEM if someone requested some unreasonable amount of symbols. And INT_MAX won't be necessary if we delegate all the overflow checking to kvmalloc_array()
[1] https://lore.kernel.org/lkml/412bf136-6a5b-f442-1e84-778697e2b694@fb.com/
if (!addrs) return -ENOMEM;-- 2.1.4