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authorWillem de Bruijn <willemb@google.com>2021-01-09 17:18:33 -0500
committerJakub Kicinski <kuba@kernel.org>2021-01-11 18:20:09 -0800
commit97550f6fa59254435d864b92603de3ca4b5a99f8 (patch)
treea2236300b4b899a2e4a34e73dffe85910f455faa /net
parent29766bcffad03da66892bef82674883e31f78fec (diff)
net: compound page support in skb_seq_read
skb_seq_read iterates over an skb, returning pointer and length of the next data range with each call. It relies on kmap_atomic to access highmem pages when needed. An skb frag may be backed by a compound page, but kmap_atomic maps only a single page. There are not enough kmap slots to always map all pages concurrently. Instead, if kmap_atomic is needed, iterate over each page. As this increases the number of calls, avoid this unless needed. The necessary condition is captured in skb_frag_must_loop. I tried to make the change as obvious as possible. It should be easy to verify that nothing changes if skb_frag_must_loop returns false. Tested: On an x86 platform with CONFIG_HIGHMEM=y CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP=y CONFIG_NETFILTER_XT_MATCH_STRING=y Run ip link set dev lo mtu 1500 iptables -A OUTPUT -m string --string 'badstring' -algo bm -j ACCEPT dd if=/dev/urandom of=in bs=1M count=20 nc -l -p 8000 > /dev/null & nc -w 1 -q 0 localhost 8000 < in Signed-off-by: Willem de Bruijn <willemb@google.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
-rw-r--r--net/core/skbuff.c28
1 files changed, 23 insertions, 5 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b6f2b520a9b7..0da035c1e53f 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3442,6 +3442,7 @@ void skb_prepare_seq_read(struct sk_buff *skb, unsigned int from,
st->root_skb = st->cur_skb = skb;
st->frag_idx = st->stepped_offset = 0;
st->frag_data = NULL;
+ st->frag_off = 0;
}
EXPORT_SYMBOL(skb_prepare_seq_read);
@@ -3496,14 +3497,27 @@ next_skb:
st->stepped_offset += skb_headlen(st->cur_skb);
while (st->frag_idx < skb_shinfo(st->cur_skb)->nr_frags) {
+ unsigned int pg_idx, pg_off, pg_sz;
+
frag = &skb_shinfo(st->cur_skb)->frags[st->frag_idx];
- block_limit = skb_frag_size(frag) + st->stepped_offset;
+ pg_idx = 0;
+ pg_off = skb_frag_off(frag);
+ pg_sz = skb_frag_size(frag);
+
+ if (skb_frag_must_loop(skb_frag_page(frag))) {
+ pg_idx = (pg_off + st->frag_off) >> PAGE_SHIFT;
+ pg_off = offset_in_page(pg_off + st->frag_off);
+ pg_sz = min_t(unsigned int, pg_sz - st->frag_off,
+ PAGE_SIZE - pg_off);
+ }
+
+ block_limit = pg_sz + st->stepped_offset;
if (abs_offset < block_limit) {
if (!st->frag_data)
- st->frag_data = kmap_atomic(skb_frag_page(frag));
+ st->frag_data = kmap_atomic(skb_frag_page(frag) + pg_idx);
- *data = (u8 *) st->frag_data + skb_frag_off(frag) +
+ *data = (u8 *)st->frag_data + pg_off +
(abs_offset - st->stepped_offset);
return block_limit - abs_offset;
@@ -3514,8 +3528,12 @@ next_skb:
st->frag_data = NULL;
}
- st->frag_idx++;
- st->stepped_offset += skb_frag_size(frag);
+ st->stepped_offset += pg_sz;
+ st->frag_off += pg_sz;
+ if (st->frag_off == skb_frag_size(frag)) {
+ st->frag_off = 0;
+ st->frag_idx++;
+ }
}
if (st->frag_data) {