diff mbox series

[SRU,F,1/3] skbuff: introduce skb_expand_head()

Message ID 20240729235145.120867-2-vinicius.peixoto@canonical.com
State New
Headers show
Series CVE-2024-26921 | expand

Commit Message

Vinicius Peixoto July 29, 2024, 11:51 p.m. UTC 
From: Vasily Averin <vvs@virtuozzo.com>

Like skb_realloc_headroom(), new helper increases headroom of specified skb.
Unlike skb_realloc_headroom(), it does not allocate a new skb if possible;
copies skb->sk on new skb when as needed and frees original skb in case
of failures.

This helps to simplify ip[6]_finish_output2() and a few other similar cases.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry-picked from commit f1260ff15a71b8fc122b2c9abd8a7abffb6e0168)
CVE-2024-26921
Signed-off-by: Vinicius Peixoto <vinicius.peixoto@canonical.com>
---
 include/linux/skbuff.h |  1 +
 net/core/skbuff.c      | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)
diff mbox series

Patch

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 29ccc33a1c627..53949a9c464e1 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1121,6 +1121,7 @@  static inline struct sk_buff *__pskb_copy(struct sk_buff *skb, int headroom,
 int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, gfp_t gfp_mask);
 struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
 				     unsigned int headroom);
+struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom);
 struct sk_buff *skb_copy_expand(const struct sk_buff *skb, int newheadroom,
 				int newtailroom, gfp_t priority);
 int __must_check skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 82be36c87eb60..115c7265c7d6c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1726,6 +1726,48 @@  struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom)
 }
 EXPORT_SYMBOL(skb_realloc_headroom);
 
+/**
+ *	skb_expand_head - reallocate header of &sk_buff
+ *	@skb: buffer to reallocate
+ *	@headroom: needed headroom
+ *
+ *	Unlike skb_realloc_headroom, this one does not allocate a new skb
+ *	if possible; copies skb->sk to new skb as needed
+ *	and frees original skb in case of failures.
+ *
+ *	It expect increased headroom and generates warning otherwise.
+ */
+
+struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
+{
+	int delta = headroom - skb_headroom(skb);
+
+	if (WARN_ONCE(delta <= 0,
+		      "%s is expecting an increase in the headroom", __func__))
+		return skb;
+
+	/* pskb_expand_head() might crash, if skb is shared */
+	if (skb_shared(skb)) {
+		struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
+
+		if (likely(nskb)) {
+			if (skb->sk)
+				skb_set_owner_w(nskb, skb->sk);
+			consume_skb(skb);
+		} else {
+			kfree_skb(skb);
+		}
+		skb = nskb;
+	}
+	if (skb &&
+	    pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
+		kfree_skb(skb);
+		skb = NULL;
+	}
+	return skb;
+}
+EXPORT_SYMBOL(skb_expand_head);
+
 /**
  *	skb_copy_expand	-	copy and expand sk_buff
  *	@skb: buffer to copy