Backport 2.28: Fix uninitialised memory access in constant time functions #5859
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Fix an issue reported by Coverity whereby some constant time functions called from the ssl decrypt code could potentially access uninitialised memory. Signed-off-by: Paul Elliott <[email protected]>
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daverodgman
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May 20, 2022
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Description
Fix an issue reported by Coverity whereby some constant time functions called from the ssl decrypt code could potentially access uninitialised memory, by zeroing memory in two of the places where this function is used.
Add a note to mbedtls_ct_memcpy_if_eq() documentation to warn that it reads from the buffer as well as writing to it. Note that no decisions are taken as a result of the uninitialised data, but obviously its still not best practice.
This is a backport of #5829
Status
READY
Migrations
NO
Additional comments
As we are not trying to hide the length that will be copied, I used memset to zero the target buffers. I hope this is not too out of place in constant_time.c, and will re-write if people feel that it is.
Todos
Steps to test or reproduce
test_suite_ssl should run clean.