[PATCH stable 6.1 5.15 5.10] bpf: Check validity of link->type in bpf_link_show_fdinfo()

[PATCH stable 6.1 5.15 5.10] bpf: Check validity of link->type in bpf_link_show_fdinfo()

[Shung-Hsi Yu]

From: Hou Tao <houtao1@huawei.com>

commit 8421d4c8762bd022cb491f2f0f7019ef51b4f0a7 upstream.

If a newly-added link type doesn't invoke BPF_LINK_TYPE(), accessing
bpf_link_type_strs[link->type] may result in an out-of-bounds access.

To spot such missed invocations early in the future, checking the
validity of link->type in bpf_link_show_fdinfo() and emitting a warning
when such invocations are missed.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241024013558.1135167-3-houtao@huaweicloud.com
[ shung-hsi.yu: break up existing seq_printf() call since commit 68b04864ca42
  ("bpf: Create links for BPF struct_ops maps.") is not present ]
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 kernel/bpf/syscall.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f9906e5ad2e5..6455f80099cd 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2816,16 +2816,21 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
 {
 	const struct bpf_link *link = filp->private_data;
 	const struct bpf_prog *prog = link->prog;
+	enum bpf_link_type type = link->type;
 	char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
 
+	if (type < ARRAY_SIZE(bpf_link_type_strs) && bpf_link_type_strs[type]) {
+		seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
+	} else {
+		WARN_ONCE(1, "missing BPF_LINK_TYPE(...) for link type %u\n", type);
+		seq_printf(m, "link_type:\t<%u>\n", type);
+	}
+	seq_printf(m, "link_id:\t%u\n", link->id);
+
 	bin2hex(prog_tag, prog->tag, sizeof(prog->tag));
 	seq_printf(m,
-		   "link_type:\t%s\n"
-		   "link_id:\t%u\n"
 		   "prog_tag:\t%s\n"
 		   "prog_id:\t%u\n",
-		   bpf_link_type_strs[link->type],
-		   link->id,
 		   prog_tag,
 		   prog->aux->id);
 	if (link->ops->show_fdinfo)
-- 
2.47.1

Re: [PATCH stable 6.1 5.15 5.10] bpf: Check validity of link->type in bpf_link_show_fdinfo()

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 8421d4c8762bd022cb491f2f0f7019ef51b4f0a7

WARNING: Author mismatch between patch and upstream commit:
Backport author: Shung-Hsi Yu<shung-hsi.yu@suse.com>
Commit author: Hou Tao<houtao1@huawei.com>


Status in newer kernel trees:
6.12.y | Present (exact SHA1)

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.12.y       |  Failed     |  N/A       |
| stable/linux-6.6.y        |  Failed     |  N/A       |
| stable/linux-6.1.y        |  Success    |  Success   |
| stable/linux-5.15.y       |  Success    |  Success   |
| stable/linux-5.10.y       |  Success    |  Success   |
| stable/linux-5.4.y        |  Failed     |  N/A       |