commit 780e498f760b139fb540d2e050de08df60714f4a Author: David Goulet dgoulet@torproject.org Date: Tue Jan 14 12:42:09 2020 -0500

hs-v3: Code improvement for INTRO2 MAC validation

Pointed by nickm during the review of #32709.

Signed-off-by: David Goulet dgoulet@torproject.org --- src/feature/hs/hs_cell.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/feature/hs/hs_cell.c b/src/feature/hs/hs_cell.c index 680897cf9..021a41825 100644 --- a/src/feature/hs/hs_cell.c +++ b/src/feature/hs/hs_cell.c @@ -776,6 +776,12 @@ get_introduce2_keys_and_verify_mac(hs_cell_introduce2_data_t *data, * in the cell is at the end of the encrypted section. */ { uint8_t mac[DIGEST256_LEN]; + + /* Make sure we are now about to underflow. */ + if (encrypted_section_len < sizeof(mac)) { + goto err; + } + /* The MAC field is at the very end of the ENCRYPTED section. */ size_t mac_offset = encrypted_section_len - sizeof(mac); /* Compute the MAC. Use the entire encoded payload with a length up to the @@ -785,7 +791,7 @@ get_introduce2_keys_and_verify_mac(hs_cell_introduce2_data_t *data, encrypted_section, encrypted_section_len, intro_keys->mac_key, sizeof(intro_keys->mac_key), mac, sizeof(mac)); - if (tor_memcmp(mac, encrypted_section + mac_offset, sizeof(mac))) { + if (tor_memneq(mac, encrypted_section + mac_offset, sizeof(mac))) { log_info(LD_REND, "Invalid MAC validation for INTRODUCE2 cell"); goto err; }