net: rename skb_unshare() to skb_unclone_full()

skb_unshare() only copies cloned skbs. A shared skb that is not a clone
comes back unchanged, which the name doesn't suggest. The loopback
selftest hooks got caught by this and hit BUG_ON(skb_shared()).

Rename it to skb_unclone_full(). Like skb_unclone() it only acts on
clones, but it copies the whole skb, not just the head.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com> # dpaa2
Link: https://patch.msgid.link/20261015-nb-skb-unclone-full-v1-1-0dfbf01f60f2@tipi-net.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 15 insertions, 12 deletions

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 975892367136..c863cdf60f01 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -427,8 +427,8 @@ static inline int __vlan_insert_tag(struct sk_buff *skb,
  * Inserts the VLAN tag into @skb as part of the payload at offset mac_len
  * Returns a VLAN tagged skb. This might change skb->head.
  *
- * Following the skb_unshare() example, in case of error, the calling function
- * doesn't have to worry about freeing the original skb.
+ * Following the skb_unclone_full() example, in case of error, the calling
+ * function doesn't have to worry about freeing the original skb.
  *
  * Does not change skb->protocol so this function can be used during receive.
  *
@@ -458,8 +458,8 @@ static inline struct sk_buff *vlan_insert_inner_tag(struct sk_buff *skb,
  * Inserts the VLAN tag into @skb as part of the payload
  * Returns a VLAN tagged skb. This might change skb->head.
  *
- * Following the skb_unshare() example, in case of error, the calling function
- * doesn't have to worry about freeing the original skb.
+ * Following the skb_unclone_full() example, in case of error, the calling
+ * function doesn't have to worry about freeing the original skb.
  *
  * Does not change skb->protocol so this function can be used during receive.
  *
@@ -480,8 +480,8 @@ static inline struct sk_buff *vlan_insert_tag(struct sk_buff *skb,
  * Inserts the VLAN tag into @skb as part of the payload
  * Returns a VLAN tagged skb. This might change skb->head.
  *
- * Following the skb_unshare() example, in case of error, the calling function
- * doesn't have to worry about freeing the original skb.
+ * Following the skb_unclone_full() example, in case of error, the calling
+ * function doesn't have to worry about freeing the original skb.
  *
  * Return: modified @skb on success, NULL on error (@skb is freed).
  */
@@ -524,8 +524,8 @@ static inline void __vlan_hwaccel_copy_tag(struct sk_buff *dst, const struct sk_
  *
  * Pushes the VLAN tag from @skb->vlan_tci inside to the payload.
  *
- * Following the skb_unshare() example, in case of error, the calling function
- * doesn't have to worry about freeing the original skb.
+ * Following the skb_unclone_full() example, in case of error, the calling
+ * function doesn't have to worry about freeing the original skb.
  */
 static inline struct sk_buff *__vlan_hwaccel_push_inside(struct sk_buff *skb)
 {
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index af1cbc2799b7..5079335f7aae 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2131,14 +2131,14 @@ static inline struct sk_buff *skb_share_check(struct sk_buff *skb, gfp_t pri)
 }
 
 /*
- *	Copy shared buffers into a new sk_buff. We effectively do COW on
+ *	Copy cloned buffers into a new sk_buff. We effectively do COW on
  *	packets to handle cases where we have a local reader and forward
  *	and a couple of other messy ones. The normal one is tcpdumping
  *	a packet that's being forwarded.
  */
 
 /**
- *	skb_unshare - make a copy of a shared buffer
+ *	skb_unclone_full - make a private copy of a cloned buffer
  *	@skb: buffer to check
  *	@pri: priority for memory allocation
  *
@@ -2148,10 +2148,13 @@ static inline struct sk_buff *skb_share_check(struct sk_buff *skb, gfp_t pri)
  *	the original buffer is returned. When called with a spinlock held or
  *	from interrupt state @pri must be %GFP_ATOMIC
  *
+ *	Unlike skb_unclone(), the paged data is copied as well. A buffer with
+ *	skb->users > 1 that is not a clone is returned as is, use
+ *	skb_share_check() for that case.
+ *
  *	%NULL is returned on a memory allocation failure.
  */
-static inline struct sk_buff *skb_unshare(struct sk_buff *skb,
-					  gfp_t pri)
+static inline struct sk_buff *skb_unclone_full(struct sk_buff *skb, gfp_t pri)
 {
 	might_sleep_if(gfpflags_allow_blocking(pri));
 	if (skb_cloned(skb)) {