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`.

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

Cc: original author cbulinaru@gmail.com in case we're overlooking a reason for the split between rtattr_add_str and rtattr_add_strsz.

the first avoids the \0 and is used for IFLA_NAME. Device names are guaranteed to fit into IFNAMSIZ, including the terminating \0.

---

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); -- 2.48.1