According to random(4) manual, /dev/random is essentially deprecated on
Linux for quite some time:
"The /dev/random interface is considered a legacy interface, and
/dev/urandom is preferred and sufficient in all use cases, with the
exception of applications which require randomness during early boot
time; for these applications, getrandom(2) must be used instead, because
it will block until the entropy pool is initialized."
An attempt to use it would cause unnecessary blocking on machines
without a good hwrng even when it shouldn't be needed. Since Linux 3.17,
a getrandom(2) call is available that will block only until the
randomness pool has been seeded.
It is probably not a good default yet as it requires a fairly recent
kernel and glibc (3.17 and 2.25 respectively).
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
ubsan reported:
../src/crypto/random.c:69:30: runtime error: shift exponent 32 is too large for 32-bit type 'unsigned int'
Explicitly check for the ROL32(x, 0) case which is supposed to be a
no-op.
Signed-off-by: Michael Braun <michael-dev@fami-braun.de>
The bytes pointer was not reset back to the beginning of the buffer when
mixing in additional entropy from the crypto module. This resulted in
writing beyond the return buffer and not getting the required mixing of
the extra entropy for the actual return buffer.
Signed-off-by: Jouni Malinen <j@w1.fi>
This converts most of the remaining perror() and printf() calls from
hostapd and wpa_supplicant to use wpa_printf().
Signed-off-by: Jouni Malinen <j@w1.fi>
Mark the debug print excessive and print it only in case the entropy
collection is used since this function can get called pretty frequently.
Signed-hostap: Jouni Malinen <j@w1.fi>
Some compilers complain about fwrite calls if the return value is
not checked, so check the value even if it does not really make
much of a difference in this particular case.
This can be used to avoid rejection of first two 4-way handshakes every
time hostapd (or wpa_supplicant in AP/IBSS mode) is restarted. A new
command line parameter, -e, can now be used to specify an entropy file
that will be used to maintain the needed state.
On Linux, verify that the kernel entropy pool is capable of providing
strong random data before allowing WPA/WPA2 connection to be
established. If 20 bytes of data cannot be read from /dev/random,
force first two 4-way handshakes to fail while collecting entropy
into the internal pool in hostapd. After that, give up on /dev/random
and allow the AP to function based on the combination of /dev/urandom
and whatever data has been collected into the internal entropy pool.
By default, make hostapd and wpa_supplicant maintain an internal
entropy pool that is fed with following information:
hostapd:
- Probe Request frames (timing, RSSI)
- Association events (timing)
- SNonce from Supplicants
wpa_supplicant:
- Scan results (timing, signal/noise)
- Association events (timing)
The internal pool is used to augment the random numbers generated
with the OS mechanism (os_get_random()). While the internal
implementation is not expected to be very strong due to limited
amount of generic (non-platform specific) information to feed the
pool, this may strengthen key derivation on some devices that are
not configured to provide strong random numbers through
os_get_random() (e.g., /dev/urandom on Linux/BSD).
This new mechanism is not supposed to replace proper OS provided
random number generation mechanism. The OS mechanism needs to be
initialized properly (e.g., hw random number generator,
maintaining entropy pool over reboots, etc.) for any of the
security assumptions to hold.
If the os_get_random() is known to provide strong ramdom data (e.g., on
Linux/BSD, the board in question is known to have reliable source of
random data from /dev/urandom), the internal hostapd random pool can be
disabled. This will save some in binary size and CPU use. However, this
should only be considered for builds that are known to be used on
devices that meet the requirements described above. The internal pool
is disabled by adding CONFIG_NO_RANDOM_POOL=y to the .config file.
Lubomir Rintel