[PATCH 5.4 060/131] bpf: Clarify error expectations from bpf_clone_redirect

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5.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stanislav Fomichev <sdf@xxxxxxxxxx>

[ Upstream commit 7cb779a6867fea00b4209bcf6de2f178a743247d ]

Commit 151e887d8ff9 ("veth: Fixing transmit return status for dropped
packets") exposed the fact that bpf_clone_redirect is capable of
returning raw NET_XMIT_XXX return codes.

This is in the conflict with its UAPI doc which says the following:
"0 on success, or a negative error in case of failure."

Update the UAPI to reflect the fact that bpf_clone_redirect can
return positive error numbers, but don't explicitly define
their meaning.

Reported-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20230911194731.286342-1-sdf@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/uapi/linux/bpf.h       | 4 +++-
 tools/include/uapi/linux/bpf.h | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index cb0631098f918..e5250a9b813d6 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -780,7 +780,9 @@ union bpf_attr {
  * 		performed again, if the helper is used in combination with
  * 		direct packet access.
  * 	Return
- * 		0 on success, or a negative error in case of failure.
+ * 		0 on success, or a negative error in case of failure. Positive
+ * 		error indicates a potential drop or congestion in the target
+ * 		device. The particular positive error codes are not defined.
  *
  * u64 bpf_get_current_pid_tgid(void)
  * 	Return
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index cb0631098f918..e5250a9b813d6 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -780,7 +780,9 @@ union bpf_attr {
  * 		performed again, if the helper is used in combination with
  * 		direct packet access.
  * 	Return
- * 		0 on success, or a negative error in case of failure.
+ * 		0 on success, or a negative error in case of failure. Positive
+ * 		error indicates a potential drop or congestion in the target
+ * 		device. The particular positive error codes are not defined.
  *
  * u64 bpf_get_current_pid_tgid(void)
  * 	Return
-- 
2.40.1






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