From: Jiangshan Yi get_subflow_info() parses the subflow address string with: char saddr[64], daddr[64]; ret = sscanf(subflow_addrs, "%[^:]:%d %[^:]:%d", saddr, &sport, daddr, &dport); The subflow_addrs buffer holds up to 1024 bytes and is taken directly from the command line ("-c" argument). The "%[^:]" conversions have no maximum field width, so if the address substring before the ':' exceeds 63 bytes, sscanf() writes past the end of the 64-byte saddr/daddr stack buffers. This overflows the stack, corrupting adjacent stack data such as the saved return address, and can crash the tool or lead to out-of-bounds writes controlled by user-supplied input. Bound both string conversions to the destination buffer size by adding an explicit maximum field width of 63 (leaving room for the terminating NUL), so at most 63 bytes are written into each 64-byte buffer: ret = sscanf(subflow_addrs, "%63[^:]:%d %63[^:]:%d", saddr, &sport, daddr, &dport); The subflow address can be passed in argument, so fixing this is helpful when the tool is manually used. Reviewed-by: Geliang Tang Signed-off-by: Jiangshan Yi Signed-off-by: Matthieu Baerts (NGI0) --- To: Shuah Khan Cc: linux-kselftest@vger.kernel.org --- tools/testing/selftests/net/mptcp/mptcp_diag.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/net/mptcp/mptcp_diag.c b/tools/testing/selftests/net/mptcp/mptcp_diag.c index 5e222ba977e4..3b8d2c8a6216 100644 --- a/tools/testing/selftests/net/mptcp/mptcp_diag.c +++ b/tools/testing/selftests/net/mptcp/mptcp_diag.c @@ -377,7 +377,8 @@ static void get_subflow_info(char *subflow_addrs) int ret; int fd; - ret = sscanf(subflow_addrs, "%[^:]:%d %[^:]:%d", saddr, &sport, daddr, &dport); + ret = sscanf(subflow_addrs, "%63[^:]:%d %63[^:]:%d", + saddr, &sport, daddr, &dport); if (ret != 4) die_perror("IP PORT Pairs has style problems!"); -- 2.53.0