From: Willem de Bruijn <will...@google.com>
skb_copy_ubufs must unclone before it is safe to modify its
skb_shared_info with skb_zcopy_clear.
Commit b90ddd568792 ("skbuff: skb_copy_ubufs must release uarg even
without user frags") ensures that all skbs release their zerocopy
state, even those without frags.
But I forgot an edge case where such an skb arrives that is cloned.
The stack does not build such packets. Vhost/tun skbs have their
frags orphaned before cloning. TCP skbs only attach zerocopy state
when a frag is added.
But if TCP packets can be trimmed or linearized, this might occur.
Tracing the code I found no instance so far (e.g., skb_linearize
ends up calling skb_zcopy_clear if !skb->data_len).
Still, it is non-obvious that no path exists. And it is fragile to
rely on this.
Fixes: b90ddd568792 ("skbuff: skb_copy_ubufs must release uarg even without
user frags")
Signed-off-by: Willem de Bruijn <will...@google.com>
---
I should have spotted this when preparing the above patch, of course.
Apologies for the added work.
Since I did not spot a path that triggers the issue, this can also
go to net-next, instead. It applies to both cleanly.
---
net/core/skbuff.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a3cb0be4c6f3..08f574081315 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1177,12 +1177,12 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
int i, new_frags;
u32 d_off;
- if (!num_frags)
- goto release;
-
if (skb_shared(skb) || skb_unclone(skb, gfp_mask))
return -EINVAL;
+ if (!num_frags)
+ goto release;
+
new_frags = (__skb_pagelen(skb) + PAGE_SIZE - 1) >> PAGE_SHIFT;
for (i = 0; i < new_frags; i++) {
page = alloc_page(gfp_mask);
--
2.15.1.620.gb9897f4670-goog
