commit 4c06c619faceb5d158a725d97fda45cadb2cf9c9 Author: Nick Mathewson <nickm@torproject.org> Date: Tue May 18 08:40:09 2021 -0400 Use a more secure hash function for the circuitmux hashtable. Fixes bug 40931; bugfix on 0.2.4.4-alpha. Also tracked as TROVE-2021-005. This issue was reported by Jann Horn from Google's Project Zero. --- changes/bug40391 | 9 +++++++++ src/core/or/circuitmux.c | 8 ++++---- 2 files changed, 13 insertions(+), 4 deletions(-) diff --git a/changes/bug40391 b/changes/bug40391 new file mode 100644 index 0000000000..e3c186275f --- /dev/null +++ b/changes/bug40391 @@ -0,0 +1,9 @@ + o Major bugfixes (security): + - Resist a hashtable-based CPU denial-of-service attack against + relays. Previously we used a naive unkeyed hash function to look up + circuits in a circuitmux object. An attacker could exploit this to + construct circuits with chosen circuit IDs in order to try to create + collisions and make the hash table inefficient. Now we use a SipHash + construction for this hash table instead. Fixes bug 40391; bugfix on + 0.2.4.4-alpha. This issue is also tracked as TROVE-2021-005. + Reported by Jann Horn from Google's Project Zero. diff --git a/src/core/or/circuitmux.c b/src/core/or/circuitmux.c index 88f9ac7923..e7309553c4 100644 --- a/src/core/or/circuitmux.c +++ b/src/core/or/circuitmux.c @@ -216,9 +216,10 @@ chanid_circid_entries_eq(chanid_circid_muxinfo_t *a, static inline unsigned int chanid_circid_entry_hash(chanid_circid_muxinfo_t *a) { - return (((unsigned int)(a->circ_id) << 8) ^ - ((unsigned int)((a->chan_id >> 32) & 0xffffffff)) ^ - ((unsigned int)(a->chan_id & 0xffffffff))); + uint8_t data[8 + 4]; + set_uint64(data, a->chan_id); + set_uint32(data + 8, a->circ_id); + return (unsigned) siphash24g(data, sizeof(data)); } /* Declare the struct chanid_circid_muxinfo_map type */ @@ -1361,4 +1362,3 @@ circuitmux_compare_muxes, (circuitmux_t *cmux_1, circuitmux_t *cmux_2)) return 0; } } -