Messages in this thread Patch in this message | | | Date | Wed, 18 May 2022 09:34:22 -0700 | Subject | Re: [PATCH bpf v3 1/2] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach | From | Yonghong Song <> |
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On 5/18/22 5:22 AM, 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. Add the same check > to kprobe_multi_resolve_syms in case it will be called from elsewhere > in the future. > > Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link") > Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com> > --- > kernel/trace/bpf_trace.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index d8553f4..212faa4 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -2352,13 +2352,15 @@ static int > kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt, > unsigned long *addrs) > { > - unsigned long addr, size; > + unsigned long addr, sym_size; > + u32 size; > const char __user **syms; > int err = -ENOMEM; > unsigned int i; > char *func; > > - size = cnt * sizeof(*syms); > + if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size)) > + return -EOVERFLOW;
In mm/util.c kvmalloc_node(), we have
/* Don't even allow crazy sizes */ if (unlikely(size > INT_MAX)) { WARN_ON_ONCE(!(flags & __GFP_NOWARN)); return NULL; }
Basically the maximum size to be allocated in INT_MAX.
Here, we have 'size' as u32, which means if the size is 0xffff0000, the check_mul_overflow will return false (no overflow) but kvzalloc will still have a warning.
I think we should change the type of 'size' to be 'int' which should catch the above case and be consistent with what kvmalloc_node() intends to warn.
> syms = kvzalloc(size, GFP_KERNEL); > if (!syms) > return -ENOMEM; > @@ -2382,9 +2384,9 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt, > addr = kallsyms_lookup_name(func); > if (!addr) > goto error; > - if (!kallsyms_lookup_size_offset(addr, &size, NULL)) > + if (!kallsyms_lookup_size_offset(addr, &sym_size, NULL)) > goto error; > - addr = ftrace_location_range(addr, addr + size - 1); > + addr = ftrace_location_range(addr, addr + sym_size - 1); > if (!addr) > goto error; > addrs[i] = addr; > @@ -2429,7 +2431,8 @@ 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;
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