From: Jakub Kicinski kuba@kernel.org
[ Upstream commit 27bc5eaf004c437309dee1b9af24806262631d57 ]
Recent changes to make netlink socket memory accounting must have broken the implicit assumption of the netlink-dump test that we can fit exactly 64 dumps into the socket. Handle the failure mode properly, and increase the dump count to 80 to make sure we still run into the error condition if the default buffer size increases in the future.
Link: https://patch.msgid.link/20250906211351.3192412-1-kuba@kernel.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
YES
Rationale - Fixes a real selftest failure mode caused by recent netlink socket memory accounting changes. The original test assumed exactly 64 dumps would fit in the socket; this is no longer reliable and leads to false failures. - The change is confined to selftests and does not affect kernel behavior or ABI, making regression risk extremely low while restoring test correctness.
Key Changes - Robust extack parsing: - Introduces explicit return semantics for control messages via `enum get_ea_ret` to distinguish done, error, and extack cases (`tools/testing/selftests/net/netlink-dumps.c:34`). - `nl_get_extack()` now treats both `NLMSG_ERROR` and `NLMSG_DONE` as control messages and returns either the base result or `FOUND_EXTACK` if TLVs are present (`tools/testing/selftests/net/netlink-dumps.c:42`, `tools/testing/selftests/net/netlink-dumps.c:55`, `tools/testing/selftests/net/netlink-dumps.c:57`, `tools/testing/selftests/net/netlink-dumps.c:64`, `tools/testing/selftests/net/netlink-dumps.c:84`, `tools/testing/selftests/net/netlink-dumps.c:87`). - Handle realistic error sequencing during dump pressure: - After intentionally overfilling the socket, the test explicitly tolerates one `ENOBUFS` and subsequent `EBUSY` responses before the final DONE+extack, matching current kernel behavior under memory pressure (`tools/testing/selftests/net/netlink-dumps.c:141`, `tools/testing/selftests/net/netlink-dumps.c:156`, `tools/testing/selftests/net/netlink-dumps.c:161`, `tools/testing/selftests/net/netlink-dumps.c:168`). - Maintain correctness checks for the intended validation error: - Still asserts the extack must carry `EINVAL` and a valid attribute offset when the invalid attribute is parsed (`tools/testing/selftests/net/netlink-dumps.c:164`, `tools/testing/selftests/net/netlink-dumps.c:165`). - Future-proofing the buffer fill: - Increases the dump count from 64 to 80 to ensure the test continues to trigger the pressure condition if default buffer sizes grow (`tools/testing/selftests/net/netlink-dumps.c:133`).
Why It Fits Stable Criteria - Important bugfix: Prevents false failures and flakiness in selftests caused by legitimate kernel changes to memory accounting. - Small and contained: Touches a single selftest file with clear, localized changes. - No features or architecture changes: Strictly test logic and robustness improvements. - Minimal regression risk: Only affects testing; improves compatibility across kernels that may return `ENOBUFS` and/or `EBUSY` under dump pressure; still verifies the original `EINVAL` extack path when applicable. - Helps keep stable trees’ selftests reliable as netlink memory accounting changes are commonly backported.
Conclusion - This is a low-risk, clearly beneficial selftest robustness fix that addresses real test failures. It should be backported to stable trees to keep networking selftests passing and meaningful.
tools/testing/selftests/net/netlink-dumps.c | 43 ++++++++++++++++----- 1 file changed, 33 insertions(+), 10 deletions(-)
diff --git a/tools/testing/selftests/net/netlink-dumps.c b/tools/testing/selftests/net/netlink-dumps.c index 07423f256f963..7618ebe528a4c 100644 --- a/tools/testing/selftests/net/netlink-dumps.c +++ b/tools/testing/selftests/net/netlink-dumps.c @@ -31,9 +31,18 @@ struct ext_ack { const char *str; };
-/* 0: no done, 1: done found, 2: extack found, -1: error */ -static int nl_get_extack(char *buf, size_t n, struct ext_ack *ea) +enum get_ea_ret { + ERROR = -1, + NO_CTRL = 0, + FOUND_DONE, + FOUND_ERR, + FOUND_EXTACK, +}; + +static enum get_ea_ret +nl_get_extack(char *buf, size_t n, struct ext_ack *ea) { + enum get_ea_ret ret = NO_CTRL; const struct nlmsghdr *nlh; const struct nlattr *attr; ssize_t rem; @@ -41,15 +50,19 @@ static int nl_get_extack(char *buf, size_t n, struct ext_ack *ea) for (rem = n; rem > 0; NLMSG_NEXT(nlh, rem)) { nlh = (struct nlmsghdr *)&buf[n - rem]; if (!NLMSG_OK(nlh, rem)) - return -1; + return ERROR;
- if (nlh->nlmsg_type != NLMSG_DONE) + if (nlh->nlmsg_type == NLMSG_ERROR) + ret = FOUND_ERR; + else if (nlh->nlmsg_type == NLMSG_DONE) + ret = FOUND_DONE; + else continue;
ea->err = -*(int *)NLMSG_DATA(nlh);
if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS)) - return 1; + return ret;
ynl_attr_for_each(attr, nlh, sizeof(int)) { switch (ynl_attr_type(attr)) { @@ -68,10 +81,10 @@ static int nl_get_extack(char *buf, size_t n, struct ext_ack *ea) } }
- return 2; + return FOUND_EXTACK; }
- return 0; + return ret; }
static const struct { @@ -99,9 +112,9 @@ static const struct { TEST(dump_extack) { int netlink_sock; + int i, cnt, ret; char buf[8192]; int one = 1; - int i, cnt; ssize_t n;
netlink_sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); @@ -118,7 +131,7 @@ TEST(dump_extack) ASSERT_EQ(n, 0);
/* Dump so many times we fill up the buffer */ - cnt = 64; + cnt = 80; for (i = 0; i < cnt; i++) { n = send(netlink_sock, &dump_neigh_bad, sizeof(dump_neigh_bad), 0); @@ -140,10 +153,20 @@ TEST(dump_extack) } ASSERT_GE(n, (ssize_t)sizeof(struct nlmsghdr));
- EXPECT_EQ(nl_get_extack(buf, n, &ea), 2); + ret = nl_get_extack(buf, n, &ea); + /* Once we fill the buffer we'll see one ENOBUFS followed + * by a number of EBUSYs. Then the last recv() will finally + * trigger and complete the dump. + */ + if (ret == FOUND_ERR && (ea.err == ENOBUFS || ea.err == EBUSY)) + continue; + EXPECT_EQ(ret, FOUND_EXTACK); + EXPECT_EQ(ea.err, EINVAL); EXPECT_EQ(ea.attr_offs, sizeof(struct nlmsghdr) + sizeof(struct ndmsg)); } + /* Make sure last message was a full DONE+extack */ + EXPECT_EQ(ret, FOUND_EXTACK); }
static const struct {