tree f9020cae8f3921e6b5d7cfeac8056159ba62f654
parent 1630888aa080f8421a2d8de1f5477c2b347ce53d
author Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> 1449741051 +0100
committer Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> 1449743035 +0100

Fix potential double free in cert writing code

In case an entry with the given OID already exists in the list passed to
mbedtls_asn1_store_named_data() and there is not enough memory to allocate
room for the new value, the existing entry will be freed but the preceding
entry in the list will sill hold a pointer to it. (And the following entries
in the list are no longer reachable.) This results in memory leak or a double
free.

The issue is we want to leave the list in a consistent state on allocation
failure. (We could add a warning that the list is left in inconsistent state
when the function returns NULL, but behaviour changes that require more care
from the user are undesirable, especially in a stable branch.)

The chosen solution is a bit inefficient in that there is a time where both
blocks are allocated, but at least it's safe and this should trump efficiency
here: this code is only used for generating certificates, which is unlikely to
be done on very constrained devices, or to be in the critical loop of
anything. Also, the sizes involved should be fairly small anyway.

fixes #367