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Backports of patch from systemd git to stable distributions
037b0a47b0
Previously we'd used the existance of a specific AF_UNIX socket in the abstract namespace as lock for disabling lookup recursions. (for breaking out of the loop: userdb synthesized from nss → nss synthesized from userdb → userdb synthesized from nss → …) I did it like that because it promised to work the same both in static and in dynmically linked environments and is accessible easily from any programming language. However, it has a weakness regarding reuse attacks: the socket is securely hashed (siphash) from the thread ID in combination with the AT_RANDOM secret. Thus it should not be guessable from an attacker in advance. That's only true if a thread takes the lock only once and keeps it forever. However, if a thread takes and releases it multiple times an attacker might monitor that and quickly take the lock after the first iteration for follow-up iterations. It's not a big issue given that userdb (as the primary user for this) never released the lock and we never made the concept a public interface, and it was only included in one release so far, but it's something that deserves fixing. (moreover it's a local DoS only, only permitting to disable native userdb lookups) With this rework the libnss_systemd.so.2 module will now export two additional symbols. These symbols are not used by glibc, but can be used by arbitrary programs: one can be used to disable nss-systemd, the other to check if it is currently disabled. The lock is per-thread. It's slightly less pretty, since it requires people to manually link against C code via dlopen()/dlsym(), but it should work safely without the aforementioned weakness. |
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catalog | ||
coccinelle | ||
docs | ||
factory/etc | ||
hwdb.d | ||
man | ||
modprobe.d | ||
network | ||
po | ||
presets | ||
rules.d | ||
semaphoreci | ||
shell-completion | ||
src | ||
sysctl.d | ||
sysusers.d | ||
test | ||
tmpfiles.d | ||
tools | ||
travis-ci | ||
units | ||
xorg | ||
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.vimrc | ||
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azure-pipelines.yml | ||
configure | ||
LICENSE.GPL2 | ||
LICENSE.LGPL2.1 | ||
Makefile | ||
meson_options.txt | ||
meson.build | ||
mkosi.build | ||
mkosi.default | ||
NEWS | ||
README | ||
README.md | ||
TODO | ||
zanata.xml |
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