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Description of problem:
The fix for CVE-2021-3712 (Ref: https://git.centos.org/rpms/openssl/blob/2906dac54f4739d3cad6c96ad5dd11fec982098b/f/SOURCES/openssl-1.0.2k-cve-2021-3712.patch#_304 ) incorrectly frees `emtmp` and destroys the target stack after *successfully* adding it to the stack. When this stack is destroyed, the pointer is freed again, causing a fault.
The root cause seems to be a logic inversion where, prior to this patch, destruction and `return 0;` happens on `!sk_OPENSSL_STRING_push(*sk, emtmp)` whereas after the patch, it happens on `sk_OPENSSL_STRING_push(*sk, emtmp)` (note the lack of negation in the latter case.
Version-Release number of selected component (if applicable):
1.0.2k-22.el7_9 vs 1.0.2k-23.el7_9
How reproducible:
This was reported by a customer of ours (MongoDB) with OCSP enabled.
Steps to Reproduce:
1. Install MongoDB 4.4.latest with RHEL7 openssl-1.0.2k-23.el7_9
2. Startup mongod with OCSP enabled.
3. Crash.
Actual results:
No crash.
Expected results:
Crash due to double free.
Additional info:
Interrestingly, upstream sources do not try to free emtmp even in the event of failure, but I suspect that's either a leak, or intentionally ignoring the use of block allocated scratch space. (Ref: https://github.com/openssl/openssl/blob/081314d07705aa58912845c213a48414d8f616a9/crypto/x509v3/v3_utl.c#L621-L626 )