[PATCH 6.12 314/567] selftests: net: fix "buffer overflow detected" for tap.c

Greg Kroah-Hartman
2026-01-06T17:31:59Z

From: Alice C. Munduruca <alice.munduruca@canonical.com>

[ Upstream commit 472c5dd6b95c02b3e5d7395acf542150e91165e7 ]

When the selftest 'tap.c' is compiled with '-D_FORTIFY_SOURCE=3',
the strcpy() in rtattr_add_strsz() is replaced with a checked
version which causes the test to consistently fail when compiled
with toolchains for which this option is enabled by default.

TAP version 13
1..3
# Starting 3 tests from 1 test cases.
# RUN tap.test_packet_valid_udp_gso ...
*** buffer overflow detected ***: terminated
# test_packet_valid_udp_gso: Test terminated by assertion
# FAIL tap.test_packet_valid_udp_gso
not ok 1 tap.test_packet_valid_udp_gso
# RUN tap.test_packet_valid_udp_csum ...
*** buffer overflow detected ***: terminated
# test_packet_valid_udp_csum: Test terminated by assertion
# FAIL tap.test_packet_valid_udp_csum
not ok 2 tap.test_packet_valid_udp_csum
# RUN tap.test_packet_crash_tap_invalid_eth_proto ...
*** buffer overflow detected ***: terminated
# test_packet_crash_tap_invalid_eth_proto: Test terminated by assertion
# FAIL tap.test_packet_crash_tap_invalid_eth_proto
not ok 3 tap.test_packet_crash_tap_invalid_eth_proto
# FAILED: 0 / 3 tests passed.
# Totals: pass:0 fail:3 xfail:0 xpass:0 skip:0 error:0

A buffer overflow is detected by the fortified glibc __strcpy_chk()
since the __builtin_object_size() of `RTA_DATA(rta)` is incorrectly
reported as 1, even though there is ample space in its bounding
buffer `req`.

Additionally, given that IFLA_IFNAME also expects a null-terminated
string, callers of rtaddr_add_str{,sz}() could simply use the
rtaddr_add_strsz() variant. (which has been renamed to remove the
trailing `sz`) memset() has been used for this function since it
is unchecked and thus circumvents the issue discussed in the
previous paragraph.

Fixes: 2e64fe4624d1 ("selftests: add few test cases for tap driver")
Signed-off-by: Alice C. Munduruca <alice.munduruca@canonical.com>
Reviewed-by: Cengiz Can <cengiz.can@canonical.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20251216170641.250494-1-alice.munduruca@canonical.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/testing/selftests/net/tap.c | 16 +++++-----------
1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/net/tap.c b/tools/testing/selftests/net/tap.c
index 247c3b3ac1c9..51a209014f1c 100644
--- a/tools/testing/selftests/net/tap.c
+++ b/tools/testing/selftests/net/tap.c
@@ -56,18 +56,12 @@ static void rtattr_end(struct nlmsghdr *nh, struct rtattr *attr)
static struct rtattr *rtattr_add_str(struct nlmsghdr *nh, unsigned short type,
const char *s)
{
- struct rtattr *rta = rtattr_add(nh, type, strlen(s));
+ unsigned int strsz = strlen(s) + 1;
+ struct rtattr *rta;

- memcpy(RTA_DATA(rta), s, strlen(s));
- return rta;
-}
-
-static struct rtattr *rtattr_add_strsz(struct nlmsghdr *nh, unsigned short type,
- const char *s)
-{
- struct rtattr *rta = rtattr_add(nh, type, strlen(s) + 1);
+ rta = rtattr_add(nh, type, strsz);

- strcpy(RTA_DATA(rta), s);
+ memcpy(RTA_DATA(rta), s, strsz);
return rta;
}

@@ -119,7 +113,7 @@ static int dev_create(const char *dev, const char *link_type,

link_info = rtattr_begin(&req.nh, IFLA_LINKINFO);

- rtattr_add_strsz(&req.nh, IFLA_INFO_KIND, link_type);
+ rtattr_add_str(&req.nh, IFLA_INFO_KIND, link_type);

if (fill_info_data) {
info_data = rtattr_begin(&req.nh, IFLA_INFO_DATA);
--
2.51.0