drbg_get_entropy: force a reseed before calling ssleay_rand_bytes() [first attempt]#7247
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mspncp wants to merge 2 commits intoopenssl:OpenSSL_1_0_2-stablefrom
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drbg_get_entropy: force a reseed before calling ssleay_rand_bytes() [first attempt]#7247mspncp wants to merge 2 commits intoopenssl:OpenSSL_1_0_2-stablefrom
mspncp wants to merge 2 commits intoopenssl:OpenSSL_1_0_2-stablefrom
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paulidale
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Sep 17, 2018
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Thanks Pauli. I'll wait for Kurts opinion nevertheless before merging. |
Fixes openssl#7240 In FIPS mode, the default FIPS DRBG uses the drbg_get_entropy() callback to reseed itself, which is provided by the wrapping libcrypto library. This callback in turn uses ssleay_rand_bytes() to generate random bytes. Now ssleay_rand_bytes() calls RAND_poll() once on first call to seed itself, but RAND_poll() is never called again (unless the application calls RAND_poll() explicitely). This implies that whenever the DRBG reseeds itself (which happens every 2^14 generate requests) this happens without obtaining fresh random data from the operating system's entropy sources. This patch forces a reseed from system entropy sources on every call to drbg_get_entropy(). In contrary to the automatic reseeding of the DRBG in master, this reseeding does not break applications running in a chroot() environment (see c7504ae), because the SSLEAY PRNG does not maintain an error state. (It does not even check the return value of RAND_poll() on its instantiation.) In the worst case, if no random device is available for reseeding, no fresh entropy will be added to the SSLEAY PRNG but it will happily continue to generate random bytes as 'entropy' input for the DRBG's reseeding, which is just as good (or bad) as before this patch.
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Just added |
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@paulidale in view of #7240 (comment) I decided to remove the note about the locking from the comment. Please reconfirm. |
paulidale
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Sep 18, 2018
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@kroeckx are you interested in reviewing this pr? |
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kaduk
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Kind of an awkward workaround, but I don't think we have scope to do broader changes on this branch.
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I didn't have time to look at this yet, just merge it.
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Closing this pull request in favour of #7259. |
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Fixes #7240
In FIPS mode, the default FIPS DRBG uses the drbg_get_entropy()
callback to reseed itself, which is provided by the wrapping
libcrypto library. This callback in turn uses ssleay_rand_bytes()
to generate random bytes.
Now ssleay_rand_bytes() calls RAND_poll() once on first call to
seed itself, but RAND_poll() is never called again (unless the
application calls RAND_poll() explicitely). This implies that
whenever the DRBG reseeds itself (which happens every 2^14
generate requests) this happens without obtaining fresh random
data from the operating system's entropy sources.
This patch forces a reseed from system entropy sources on every
call to drbg_get_entropy(). In contrary to the automatic reseeding
of the DRBG in master, this reseeding does not break applications
running in a chroot() environment (see c7504ae), because the
SSLEAY PRNG does not maintain an error state. (It does not even
check the return value of RAND_poll() on its instantiation.)
In the worst case, if no random device is available for reseeding,
no fresh entropy will be added to the SSLEAY PRNG but it will happily
continue to generate random bytes as 'entropy' input for the DRBG's
reseeding, which is just as good (or bad) as before this patch.
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