Miroslav Lichvar pushed to branch master at chrony / chrony
Commits: dab98fa8 by Miroslav Lichvar at 2025-04-03T16:05:04+02:00 util: add function for constant-time memory comparison Add a function to check if two buffers of the same length contain the same data, but do the comparison in a constant time with respect to the returned value to avoid creating a timing side channel, i.e. the time depends only on the buffer length, not on the content. Use the gnutls_memcmp() or nettle_memeql_sec() functions if available, otherwise use the same algorithm as nettle - bitwise ORing XORed data. - - - - - d115449e by Miroslav Lichvar at 2025-04-03T16:27:02+02:00 keys: compare MACs in constant time Switch from memcmp() to the new constant-time function to compare the received and expected authentication data generated with a symmetric key (NTP MAC or AES CMAC). While this doesn't seem to be strictly necessary with the current code, it is a recommended practice to prevent timing attacks. If memcmp() compared the MACs one byte at a time (a typical memcmp() implementation works with wider integers for better performance) and chronyd as an NTP client/server/peer was leaking the timing of the comparison (e.g. in the monitoring protocol), an attacker might be able for a given NTP request or response find in a sequence the individual bytes of the MAC by observing differences in the timing over a large number of attempts. However, this process would likely be so slow the authenticated request or response would not be useful in a MITM attack as the expected origin timestamp is changing with each poll. Extend the keys unit test to compare the time the function takes to compare two identical MACs and MACs differing in the first byte (maximizing the timing difference). It should fail if the compiler's optimizations figure out the function can return early. The test is not included in the util unit test to avoid compile-time optimizations with the function and its caller together. The test can be disabled by setting NO_TIMING_TESTS environment variable if it turns out to be unreliable. - - - - - f7daec06 by Miroslav Lichvar at 2025-04-03T16:27:26+02:00 sys_timex: detect clock interference from other processes After an ntp_adjtime()/adjtimex() call, check if the frequency, PLL time constant and PLL status are as expected from the previous call. If they changed, log a warning message to indicate that another NTP client might be running on the system and interfering with the system clock. - - - - - 7 changed files: - configure - keys.c - sys_timex.c - test/unit/keys.c - test/unit/util.c - util.c - util.h View it on GitLab: https://gitlab.com/chrony/chrony/-/compare/dd8738119bf9228cc718f2f67091efcd428a2970...f7daec0693aee108866134a08c6f881c18502156 -- View it on GitLab: https://gitlab.com/chrony/chrony/-/compare/dd8738119bf9228cc718f2f67091efcd428a2970...f7daec0693aee108866134a08c6f881c18502156 You're receiving this email because of your account on gitlab.com.
