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coredump: use %d in kernel core pattern

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The kernel provides %d which is documented as
"dump mode—same as value returned by prctl(2) PR_GET_DUMPABLE".

We already query /proc/pid/auxv for this information, but unfortunately this
check is subject to a race, because the crashed process may be replaced by an
attacker before we read this data, for example replacing a SUID process that
was killed by a signal with another process that is not SUID, tricking us into
making the coredump of the original process readable by the attacker.

With this patch, we effectively add one more check to the list of conditions
that need be satisfied if we are to make the coredump accessible to the user.

Reportedy-by: Qualys Security Advisory <qsa@qualys.com>

In principle, %d might return a value other than 0, 1, or 2 in the future.
Thus, we accept those, but emit a notice.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2025-04-29 14:47:59 +02:00
parent 49f1f2d4a7
commit 0c49e0049b
4 changed files with 36 additions and 4 deletions
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2
sysctl.d/50-coredump.conf.in
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@@ -13,7 +13,7 @@
# the core dump.
#
# See systemd-coredump(8) and core(5).
kernel.core_pattern=|{{LIBEXECDIR}}/systemd-coredump %P %u %g %s %t %c %h
kernel.core_pattern=|{{LIBEXECDIR}}/systemd-coredump %P %u %g %s %t %c %h %d
# Allow 16 coredumps to be dispatched in parallel by the kernel.
# We collect metadata from /proc/%P/, and thus need to make sure the crashed