Re: [PATCH net] bpf: test_run: fix WARNING in format_decode

[Daniel Borkmann]

On 11/22/23 6:28 AM, Yonghong Song wrote:

On 11/21/23 7:50 PM, Edward Adam Davis wrote:

Confirm that skb->len is not 0 to ensure that skb length is valid.

Fixes: 114039b34201 ("bpf: Move skb->len == 0 checks into __bpf_redirect")
Reported-by: syzbot+e2c932aec5c8a6e1d...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis 


Stan, Could you take a look at this patch?


I think this only papers over the bug.. also BPF selftests seem to break
with this change.

Looking again at the syzkaller trace :

  [...]
  Please remove unsupported %\0 in format string
  WARNING: CPU: 0 PID: 5068 at lib/vsprintf.c:2675 format_decode+0xa03/0xba0 
lib/vsprintf.c:2675
  [...]

We need to fix bpf_bprintf_prepare() instead to reject invalid fmts such
as %0 and similar.


  net/bpf/test_run.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index c9fdcc5cdce1..78258a822a5c 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -845,6 +845,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct 
__sk_buff *__skb)
  {
  struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb;
+    if (!skb->len)
+    return -EINVAL;
+
  if (!__skb)
  return 0;

Re: [PATCH net] bpf: test_run: fix WARNING in format_decode

[Yonghong Song]

On 11/21/23 7:50 PM, Edward Adam Davis wrote:

Confirm that skb->len is not 0 to ensure that skb length is valid.

Fixes: 114039b34201 ("bpf: Move skb->len == 0 checks into __bpf_redirect")
Reported-by: syzbot+e2c932aec5c8a6e1d...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis 


Stan, Could you take a look at this patch?



---
  net/bpf/test_run.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index c9fdcc5cdce1..78258a822a5c 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -845,6 +845,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct 
__sk_buff *__skb)
  {
struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb;
  
+	if (!skb->len)

+   return -EINVAL;
+
if (!__skb)
return 0;
  

[PATCH net] bpf: test_run: fix WARNING in format_decode

[Edward Adam Davis]

Confirm that skb->len is not 0 to ensure that skb length is valid.

Fixes: 114039b34201 ("bpf: Move skb->len == 0 checks into __bpf_redirect")
Reported-by: syzbot+e2c932aec5c8a6e1d...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis 
---
 net/bpf/test_run.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index c9fdcc5cdce1..78258a822a5c 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -845,6 +845,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct 
__sk_buff *__skb)
 {
struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb;
 
+   if (!skb->len)
+   return -EINVAL;
+
if (!__skb)
return 0;
 
-- 
2.26.1