[PATCH] netrom: fix double-free in nr_route_frame()
From: Jeongjun Park <hidden>
Date: 2026-01-19 06:34:35
Also in:
linux-hams, lkml, stable
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
In nr_route_frame(), old_skb is immediately freed without checking if nr_neigh->ax25 pointer is NULL. Therefore, if nr_neigh->ax25 is NULL, the caller function will free old_skb again, causing a double-free bug. Therefore, to prevent this, we need to modify it to check whether nr_neigh->ax25 is NULL before freeing old_skb. Cc: <redacted> Reported-by: syzbot+999115c3bf275797dc27@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/69694d6f.050a0220.58bed.0029.GAE@google.com/ (local) Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Jeongjun Park <redacted> --- net/netrom/nr_route.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/net/netrom/nr_route.c b/net/netrom/nr_route.c
index b94cb2ffbaf8..9cc29ae85b06 100644
--- a/net/netrom/nr_route.c
+++ b/net/netrom/nr_route.c@@ -752,7 +752,7 @@ int nr_route_frame(struct sk_buff *skb, ax25_cb *ax25) unsigned char *dptr; ax25_cb *ax25s; int ret; - struct sk_buff *skbn; + struct sk_buff *nskb, *oskb; /* * Reject malformed packets early. Check that it contains at least 2
@@ -811,14 +811,16 @@ int nr_route_frame(struct sk_buff *skb, ax25_cb *ax25) /* We are going to change the netrom headers so we should get our own skb, we also did not know until now how much header space we had to reserve... - RXQ */ - if ((skbn=skb_copy_expand(skb, dev->hard_header_len, 0, GFP_ATOMIC)) == NULL) { + nskb = skb_copy_expand(skb, dev->hard_header_len, 0, GFP_ATOMIC); + + if (!nskb) { nr_node_unlock(nr_node); nr_node_put(nr_node); dev_put(dev); return 0; } - kfree_skb(skb); - skb=skbn; + oskb = skb; + skb = nskb; skb->data[14]--; dptr = skb_push(skb, 1);
@@ -837,6 +839,9 @@ int nr_route_frame(struct sk_buff *skb, ax25_cb *ax25) nr_node_unlock(nr_node); nr_node_put(nr_node); + if (ret) + kfree_skb(oskb); + return ret; } --