net: add support for skbs with unreadable frags

For device memory TCP, we expect the skb headers to be available in host
memory for access, and we expect the skb frags to be in device memory
and unaccessible to the host. We expect there to be no mixing and
matching of device memory frags (unaccessible) with host memory frags
(accessible) in the same skb.

Add a skb->devmem flag which indicates whether the frags in this skb
are device memory frags or not.

__skb_fill_netmem_desc() now checks frags added to skbs for net_iov,
and marks the skb as skb->devmem accordingly.

Add checks through the network stack to avoid accessing the frags of
devmem skbs and avoid coalescing devmem skbs with non devmem skbs.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Kaiyuan Zhang <kaiyuanz@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20240910171458.219195-9-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 41 insertions, 2 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 671c456b93f5..74149dc4ee31 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1972,6 +1972,9 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
 	if (skb_shared(skb) || skb_unclone(skb, gfp_mask))
 		return -EINVAL;
 
+	if (!skb_frags_readable(skb))
+		return -EFAULT;
+
 	if (!num_frags)
 		goto release;
 
@@ -2145,6 +2148,9 @@ struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
 	unsigned int size;
 	int headerlen;
 
+	if (!skb_frags_readable(skb))
+		return NULL;
+
 	if (WARN_ON_ONCE(skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST))
 		return NULL;
 
@@ -2483,6 +2489,9 @@ struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
 	struct sk_buff *n;
 	int oldheadroom;
 
+	if (!skb_frags_readable(skb))
+		return NULL;
+
 	if (WARN_ON_ONCE(skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST))
 		return NULL;
 
@@ -2827,6 +2836,9 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta)
 	 */
 	int i, k, eat = (skb->tail + delta) - skb->end;
 
+	if (!skb_frags_readable(skb))
+		return NULL;
+
 	if (eat > 0 || skb_cloned(skb)) {
 		if (pskb_expand_head(skb, 0, eat > 0 ? eat + 128 : 0,
 				     GFP_ATOMIC))
@@ -2980,6 +2992,9 @@ int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
 		to     += copy;
 	}
 
+	if (!skb_frags_readable(skb))
+		goto fault;
+
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 		int end;
 		skb_frag_t *f = &skb_shinfo(skb)->frags[i];
@@ -3168,6 +3183,9 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
 	/*
 	 * then map the fragments
 	 */
+	if (!skb_frags_readable(skb))
+		return false;
+
 	for (seg = 0; seg < skb_shinfo(skb)->nr_frags; seg++) {
 		const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];
 
@@ -3391,6 +3409,9 @@ int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len)
 		from += copy;
 	}
 
+	if (!skb_frags_readable(skb))
+		goto fault;
+
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 		int end;
@@ -3470,6 +3491,9 @@ __wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
 		pos	= copy;
 	}
 
+	if (WARN_ON_ONCE(!skb_frags_readable(skb)))
+		return 0;
+
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 		int end;
 		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
@@ -3570,6 +3594,9 @@ __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset,
 		pos	= copy;
 	}
 
+	if (!skb_frags_readable(skb))
+		return 0;
+
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 		int end;
 
@@ -4061,6 +4088,7 @@ static inline void skb_split_inside_header(struct sk_buff *skb,
 		skb_shinfo(skb1)->frags[i] = skb_shinfo(skb)->frags[i];
 
 	skb_shinfo(skb1)->nr_frags = skb_shinfo(skb)->nr_frags;
+	skb1->unreadable	   = skb->unreadable;
 	skb_shinfo(skb)->nr_frags  = 0;
 	skb1->data_len		   = skb->data_len;
 	skb1->len		   += skb1->data_len;
@@ -4108,6 +4136,8 @@ static inline void skb_split_no_header(struct sk_buff *skb,
 		pos += size;
 	}
 	skb_shinfo(skb1)->nr_frags = k;
+
+	skb1->unreadable = skb->unreadable;
 }
 
 /**
@@ -4345,6 +4375,9 @@ next_skb:
 		return block_limit - abs_offset;
 	}
 
+	if (!skb_frags_readable(st->cur_skb))
+		return 0;
+
 	if (st->frag_idx == 0 && !st->frag_data)
 		st->stepped_offset += skb_headlen(st->cur_skb);
 
@@ -5992,7 +6025,10 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
 	if (to->pp_recycle != from->pp_recycle)
 		return false;
 
-	if (len <= skb_tailroom(to)) {
+	if (skb_frags_readable(from) != skb_frags_readable(to))
+		return false;
+
+	if (len <= skb_tailroom(to) && skb_frags_readable(from)) {
 		if (len)
 			BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
 		*delta_truesize = 0;
@@ -6169,6 +6205,9 @@ int skb_ensure_writable(struct sk_buff *skb, unsigned int write_len)
 	if (!pskb_may_pull(skb, write_len))
 		return -ENOMEM;
 
+	if (!skb_frags_readable(skb))
+		return -EFAULT;
+
 	if (!skb_cloned(skb) || skb_clone_writable(skb, write_len))
 		return 0;
 
@@ -6848,7 +6887,7 @@ void skb_condense(struct sk_buff *skb)
 {
 	if (skb->data_len) {
 		if (skb->data_len > skb->end - skb->tail ||
-		    skb_cloned(skb))
+		    skb_cloned(skb) || !skb_frags_readable(skb))
 			return;
 
 		/* Nice, we can free page frag(s) right now */