[PATCH bpf] bpf: fix a buffer out-of-bound access when filling raw_tp link_info

[PATCH bpf] bpf: fix a buffer out-of-bound access when filling raw_tp link_info

[Yonghong Song]

Commit f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
added link query for raw_tp. One of fields in link_info is to
fill a user buffer with tp_name. The Scurrent checking only
declares "ulen && !ubuf" as invalid. So "!ulen && ubuf" will be
valid. Later on, we do "copy_to_user(ubuf, tp_name, ulen - 1)" which
may overwrite user memory incorrectly.

This patch fixed the problem by disallowing "!ulen && ubuf" case as well.

Fixes: f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
Cc: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 kernel/bpf/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 86299a292214..ac6c784c0576 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2634,7 +2634,7 @@ static int bpf_raw_tp_link_fill_link_info(const struct bpf_link *link,
 	u32 ulen = info->raw_tracepoint.tp_name_len;
 	size_t tp_len = strlen(tp_name);
 
-	if (ulen && !ubuf)
+	if (!ulen ^ !ubuf)
 		return -EINVAL;
 
 	info->raw_tracepoint.tp_name_len = tp_len + 1;
-- 
2.24.1

Re: [PATCH bpf] bpf: fix a buffer out-of-bound access when filling raw_tp link_info

[Andrii Nakryiko]

On Fri, Aug 21, 2020 at 12:11 PM Yonghong Song <yhs@fb.com> wrote:
>
> Commit f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
> added link query for raw_tp. One of fields in link_info is to
> fill a user buffer with tp_name. The Scurrent checking only
> declares "ulen && !ubuf" as invalid. So "!ulen && ubuf" will be
> valid. Later on, we do "copy_to_user(ubuf, tp_name, ulen - 1)" which
> may overwrite user memory incorrectly.
>
> This patch fixed the problem by disallowing "!ulen && ubuf" case as well.
>
> Fixes: f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
> Cc: Andrii Nakryiko <andriin@fb.com>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  kernel/bpf/syscall.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 86299a292214..ac6c784c0576 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2634,7 +2634,7 @@ static int bpf_raw_tp_link_fill_link_info(const struct bpf_link *link,
>         u32 ulen = info->raw_tracepoint.tp_name_len;
>         size_t tp_len = strlen(tp_name);
>
> -       if (ulen && !ubuf)
> +       if (!ulen ^ !ubuf)
>                 return -EINVAL;

I think my original idea was to allow ulen == 0 && ubuf != NULL as a
still valid way to get real ulen, but it's clearly wrong with ulen-1
below. So instead of special-casing ulen==0 for the case I wanted to
support, it's easier to disallow ulen==0 && ubuf!=NULL.

So thanks for the fix!

Acked-by: Andrii Nakryiko <andriin@fb.com>

>
>         info->raw_tracepoint.tp_name_len = tp_len + 1;
> --
> 2.24.1
>

Re: [PATCH bpf] bpf: fix a buffer out-of-bound access when filling raw_tp link_info

[Alexei Starovoitov]

On Fri, Aug 21, 2020 at 1:09 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Aug 21, 2020 at 12:11 PM Yonghong Song <yhs@fb.com> wrote:
> >
> > Commit f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
> > added link query for raw_tp. One of fields in link_info is to
> > fill a user buffer with tp_name. The Scurrent checking only
> > declares "ulen && !ubuf" as invalid. So "!ulen && ubuf" will be
> > valid. Later on, we do "copy_to_user(ubuf, tp_name, ulen - 1)" which
> > may overwrite user memory incorrectly.
> >
> > This patch fixed the problem by disallowing "!ulen && ubuf" case as well.
> >
> > Fixes: f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
> > Cc: Andrii Nakryiko <andriin@fb.com>
> > Signed-off-by: Yonghong Song <yhs@fb.com>
> > ---
> >  kernel/bpf/syscall.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 86299a292214..ac6c784c0576 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -2634,7 +2634,7 @@ static int bpf_raw_tp_link_fill_link_info(const struct bpf_link *link,
> >         u32 ulen = info->raw_tracepoint.tp_name_len;
> >         size_t tp_len = strlen(tp_name);
> >
> > -       if (ulen && !ubuf)
> > +       if (!ulen ^ !ubuf)
> >                 return -EINVAL;
>
> I think my original idea was to allow ulen == 0 && ubuf != NULL as a
> still valid way to get real ulen, but it's clearly wrong with ulen-1
> below. So instead of special-casing ulen==0 for the case I wanted to
> support, it's easier to disallow ulen==0 && ubuf!=NULL.
>
> So thanks for the fix!
>
> Acked-by: Andrii Nakryiko <andriin@fb.com>

Applied. Thanks