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* [PATCH net v2 1/1] net: nsh: limit recursive GSO redispatch
@ 2026-05-10  6:58 Ren Wei
  2026-05-10 11:45 ` [syzbot ci] " syzbot ci
  0 siblings, 1 reply; 2+ messages in thread
From: Ren Wei @ 2026-05-10  6:58 UTC (permalink / raw)
  To: netdev, matttbe
  Cc: jbenc, davem, yuantan098, yifanwucs, tomapufckgml, bird, lkp,
	lx24, caoruide123, n05ec

From: Ruide Cao <caoruide123@gmail.com>

nsh_gso_segment() currently redispatches the inner payload through
skb_mac_gso_segment() after stripping one NSH header. For nested NSH
payloads, this can recurse back into nsh_gso_segment() through repeated
GSO redispatch.

The existing validation added by commit af50e4ba34f4 ("nsh: fix infinite
loop") only covers invalid header lengths and does not prevent recursive
redispatch across nested NSH payload chains.

Use the existing dev_xmit_recursion mechanism to bound recursive
redispatch, as with other nested tunnel-like paths in the networking
stack. If the recursion limit is exceeded, abort segmentation and unwind
the skb state through the existing error path.

This keeps the existing protocol behavior for normal packets while
preventing pathological recursion without adding NSH-specific protocol
unrolling.

Fixes: c411ed854584 ("nsh: add GSO support")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202604302359.kU59LnTI-lkp@intel.com/
Co-developed-by: Xiao Liu <lx24@stu.ynu.edu.cn>
Signed-off-by: Xiao Liu <lx24@stu.ynu.edu.cn>
Signed-off-by: Ruide Cao <caoruide123@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
---
changes in v2:
- Rework the fix to use dev_xmit_recursion() instead of iteratively
    unwrapping nested NSH payloads.
- Abort segmentation when the recursion limit is exceeded and unwind
    skb state through skb_gso_error_unwind().
- Rewrite the commit message to reflect the recursion-limit approach.
- v1 link: https://lore.kernel.org/all/6112cce99b4e3571444a616d0fb19e91e2fcca72.1776597598.git.caoruide123@gmail.com/

 net/nsh/nsh.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/nsh/nsh.c b/net/nsh/nsh.c
index bfb7758063f3..d83e4e2da41e 100644
--- a/net/nsh/nsh.c
+++ b/net/nsh/nsh.c
@@ -107,12 +107,14 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
 	skb->protocol = proto;
 
 	features &= NETIF_F_SG;
+	if (dev_xmit_recursion())
+		goto err;
+
+	dev_xmit_recursion_inc();
 	segs = skb_mac_gso_segment(skb, features);
-	if (IS_ERR_OR_NULL(segs)) {
-		skb_gso_error_unwind(skb, htons(ETH_P_NSH), nsh_len,
-				     mac_offset, mac_len);
-		goto out;
-	}
+	dev_xmit_recursion_dec();
+	if (IS_ERR_OR_NULL(segs))
+		goto err;
 
 	for (skb = segs; skb; skb = skb->next) {
 		skb->protocol = outer_proto;
@@ -122,6 +124,11 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
 		skb->mac_len = mac_len;
 	}
 
+	goto out;
+
+err:
+	skb_gso_error_unwind(skb, outer_proto, nsh_len, mac_offset, mac_len);
+
 out:
 	return segs;
 }
-- 
2.34.1


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