diff mbox series

[bpf,v2,1/4] bpf: Check negative offsets in __bpf_skb_min_len()

Message ID 20241129012221.739069-2-xiyou.wangcong@gmail.com (mailing list archive)
State New
Delegated to: BPF
Headers show
Series bpf: a bug fix and test cases for bpf_skb_change_tail() | expand

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netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 3 this patch: 3
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 13 maintainers not CCed: kuba@kernel.org kpsingh@kernel.org andrii@kernel.org jolsa@kernel.org eddyz87@gmail.com song@kernel.org haoluo@google.com yonghong.song@linux.dev martin.lau@linux.dev horms@kernel.org pabeni@redhat.com edumazet@google.com sdf@fomichev.me
netdev/build_clang success Errors and warnings before: 3 this patch: 3
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Commit Message

Cong Wang Nov. 29, 2024, 1:22 a.m. UTC 
From: Cong Wang <cong.wang@bytedance.com>

skb_network_offset() and skb_transport_offset() can be negative when
they are called after we pull the transport header, for example, when
we use eBPF sockmap at the point of ->sk_data_ready().

__bpf_skb_min_len() uses an unsigned int to get these offsets, this
leads to a very large number which then causes bpf_skb_change_tail()
failed unexpectedly.

Fix this by using a signed int to get these offsets and ensure the
minimum is at least zero.

Fixes: 5293efe62df8 ("bpf: add bpf_skb_change_tail helper")
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
---
 net/core/filter.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/net/core/filter.c b/net/core/filter.c
index 6625b3f563a4..c1982fd04b25 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3734,13 +3734,22 @@  static const struct bpf_func_proto bpf_skb_adjust_room_proto = {
 
 static u32 __bpf_skb_min_len(const struct sk_buff *skb)
 {
-	u32 min_len = skb_network_offset(skb);
+	int offset = skb_network_offset(skb);
+	u32 min_len = 0;
 
-	if (skb_transport_header_was_set(skb))
-		min_len = skb_transport_offset(skb);
-	if (skb->ip_summed == CHECKSUM_PARTIAL)
-		min_len = skb_checksum_start_offset(skb) +
-			  skb->csum_offset + sizeof(__sum16);
+	if (offset > 0)
+		min_len = offset;
+	if (skb_transport_header_was_set(skb)) {
+		offset = skb_transport_offset(skb);
+		if (offset > 0)
+			min_len = offset;
+	}
+	if (skb->ip_summed == CHECKSUM_PARTIAL) {
+		offset = skb_checksum_start_offset(skb) +
+			 skb->csum_offset + sizeof(__sum16);
+		if (offset > 0)
+			min_len = offset;
+	}
 	return min_len;
 }