Alice C. Munduruca wrote:

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`.

Using the unchecked function memcpy() here instead allows us to match the way rtattr_add_str() is written while avoiding the spurious test failure.

Fixes: 2e64fe4624d1 ("selftests: add few test cases for tap driver") Signed-off-by: Alice C. Munduruca alice.munduruca@canonical.com

---

tools/testing/selftests/net/tap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/tap.c b/tools/testing/selftests/net/tap.c index 247c3b3ac1c9..dd961b629295 100644 --- a/tools/testing/selftests/net/tap.c +++ b/tools/testing/selftests/net/tap.c @@ -67,7 +67,7 @@ static struct rtattr *rtattr_add_strsz(struct nlmsghdr *nh, unsigned short type, { struct rtattr *rta = rtattr_add(nh, type, strlen(s) + 1);

• strcpy(RTA_DATA(rta), s);

• memcpy(RTA_DATA(rta), s, strlen(s) + 1);

Could call strlen(s) only once in the function.

Why does rtattr_add_str do the same without the terminating '\0'? It is only used with IFNAME so assumes max size of IFNAMSIZ perhaps?

return rta; } -- 2.48.1