[PATCH bpf 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[PATCH bpf 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[Eugene Syromiatnikov]

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 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d8553f4..e90c4ce7 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2358,6 +2358,8 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
 	unsigned int i;
 	char *func;
 
+	if (check_mul_overflow(cnt, sizeof(*syms), &size))
+		return -EOVERFLOW;
 	size = cnt * sizeof(*syms);
 	syms = kvzalloc(size, GFP_KERNEL);
 	if (!syms)
@@ -2429,6 +2431,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (!cnt)
 		return -EINVAL;
 
+	if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
+		return -EOVERFLOW;
 	size = cnt * sizeof(*addrs);
 	addrs = kvmalloc(size, GFP_KERNEL);
 	if (!addrs)
-- 
2.1.4

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

[Jiri Olsa]

On Mon, May 16, 2022 at 08:27:08PM +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.  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 | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d8553f4..e90c4ce7 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2358,6 +2358,8 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
>  	unsigned int i;
>  	char *func;
>  
> +	if (check_mul_overflow(cnt, sizeof(*syms), &size))
> +		return -EOVERFLOW;

there was an update already:

  0236fec57a15 bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link

so this won't apply anymore, could you please rebase on top of the latest bpf-next/master?

thanks,
jirka

>  	size = cnt * sizeof(*syms);
>  	syms = kvzalloc(size, GFP_KERNEL);
>  	if (!syms)
> @@ -2429,6 +2431,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>  	if (!cnt)
>  		return -EINVAL;
>  
> +	if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
> +		return -EOVERFLOW;
>  	size = cnt * sizeof(*addrs);
>  	addrs = kvmalloc(size, GFP_KERNEL);
>  	if (!addrs)
> -- 
> 2.1.4
> 

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

[Eugene Syromiatnikov]

On Mon, May 16, 2022 at 11:34:45PM +0200, Jiri Olsa wrote:
> On Mon, May 16, 2022 at 08:27:08PM +0200, Eugene Syromiatnikov wrote:
> > +	if (check_mul_overflow(cnt, sizeof(*syms), &size))
> > +		return -EOVERFLOW;
> 
> there was an update already:
> 
>   0236fec57a15 bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link
> 
> so this won't apply anymore, could you please rebase on top of the latest bpf-next/master?

The issue that this specific check has to go in 4.18, as it covers
possible out-of-bounds write, I'm not sure how to handle it, have
a branch where it is merged manually?

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

[Alexei Starovoitov]

On Tue, May 17, 2022 at 12:49:34AM +0200, Eugene Syromiatnikov wrote:
> On Mon, May 16, 2022 at 11:34:45PM +0200, Jiri Olsa wrote:
> > On Mon, May 16, 2022 at 08:27:08PM +0200, Eugene Syromiatnikov wrote:
> > > +	if (check_mul_overflow(cnt, sizeof(*syms), &size))
> > > +		return -EOVERFLOW;
> > 
> > there was an update already:
> > 
> >   0236fec57a15 bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link
> > 
> > so this won't apply anymore, could you please rebase on top of the latest bpf-next/master?
> 
> The issue that this specific check has to go in 4.18, as it covers
> possible out-of-bounds write, I'm not sure how to handle it, have
> a branch where it is merged manually?

As Jiri said, please use bpf-next.