Improve DST handling (Bug 23102, Bug 21942, Bug 18018, Bug 23259).

System Internals / glibc - Carlos O'Donell [] - 12 June 2018 15:07 EDT

This commit improves DST handling significantly in the following ways: firstly is_dst () is overhauled to correctly process DST sequences that would be accepted given the ELF gABI. This means that we actually now accept slightly more sequences than before. Now we accept $ORIGIN$ORIGIN, but in the past we accepted only $ORIGIN\0 or $ORIGIN/..., but this kind of behaviour results in unexpected and uninterpreted DST sequences being used as literal search paths leading to security defects. Therefore the first step in correcting this defect is making is_dst () properly account for all DSTs and making the function context free in the sense that it counts DSTs without knowledge of path, or AT_SECURE. Next, _dl_dst_count () is also simplified to count all DSTs regardless of context. Then in _dl_dst_substitute () we reintroduce context-dependent processing for such things as AT_SECURE handling. At the level of _dl_dst_substitute we can have access to things like the true start of the string sequence to validate $ORIGIN-based paths rooted in trusted directories. Lastly, we tighten up the accepted sequences in AT_SECURE, and avoid leaving known unexpanded DSTs, this is noted in the NEWS entry.

Verified with a sequence of 68 tests on x86_64 that cover non-AT_SECURE and AT_SECURE testing using a sysroot (requires root to run). The tests cover cases for bug 23102, bug 21942, bug 18018, and bug 23259. These tests are not yet appropriate for the glibc regression testsuite, but with the upcoming test-in-container testing framework it should be possible to include these tests upstream soon.

See the mailing list for the tests:

5aad5f6178 Improve DST handling (Bug 23102, Bug 21942, Bug 18018, Bug 23259).
ChangeLog | 19 ++++++
NEWS | 11 +++
elf/dl-deps.c | 2 +-
elf/dl-dst.h | 13 ----
elf/dl-load.c | 213 ++++++++++++++++++++++++++++++++++++----------------------
5 files changed, 165 insertions(+), 93 deletions(-)


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