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systemd/0477-coredump-use-d-in-kernel-core-pattern.patch
Jan Macku cbf9da6b59 systemd-257-17 
Resolves: RHEL-126456,RHEL-109832,RHEL-109902,RHEL-112205,RHEL-113920,RHEL-120177,RHEL-72813
2025-11-05 12:27:16 +01:00

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From ca6244bc21757a799cbc81090cda3a85aa183325 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Tue, 29 Apr 2025 14:47:59 +0200
Subject: [PATCH] coredump: use %d in kernel core pattern
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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>
(cherry picked from commit 0c49e0049b7665bb7769a13ef346fef92e1ad4d6)
Related: RHEL-104135
---
man/systemd-coredump.xml | 12 ++++++++++++
src/coredump/coredump.c | 21 ++++++++++++++++++---
sysctl.d/50-coredump.conf.in | 2 +-
test/units/TEST-87-AUX-UTILS-VM.coredump.sh | 5 +++++
4 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/man/systemd-coredump.xml b/man/systemd-coredump.xml
index 737b80de9a..0f5ccf12f9 100644
--- a/man/systemd-coredump.xml
+++ b/man/systemd-coredump.xml
@@ -292,6 +292,18 @@ COREDUMP_FILENAME=/var/lib/systemd/coredump/core.Web….552351.….zst
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><varname>COREDUMP_DUMPABLE=</varname></term>
+
+ <listitem><para>The <constant>PR_GET_DUMPABLE</constant> field as reported by the kernel, see
+ <citerefentry
+ project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
+ </para>
+
+ <xi:include href="version-info.xml" xpointer="v258"/>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term><varname>COREDUMP_OPEN_FDS=</varname></term>
diff --git a/src/coredump/coredump.c b/src/coredump/coredump.c
index ac1e1cb9d3..19d4d02437 100644
--- a/src/coredump/coredump.c
+++ b/src/coredump/coredump.c
@@ -108,6 +108,7 @@ typedef enum {
_META_ARGV_REQUIRED,
/* The fields below were added to kernel/core_pattern at later points, so they might be missing. */
META_ARGV_HOSTNAME = _META_ARGV_REQUIRED, /* %h: hostname */
+ META_ARGV_DUMPABLE, /* %d: as set by the kernel */
/* If new fields are added, they should be added here, to maintain compatibility
* with callers which don't know about the new fields. */
_META_ARGV_MAX,
@@ -136,6 +137,7 @@ static const char * const meta_field_names[_META_MAX] = {
[META_ARGV_TIMESTAMP] = "COREDUMP_TIMESTAMP=",
[META_ARGV_RLIMIT] = "COREDUMP_RLIMIT=",
[META_ARGV_HOSTNAME] = "COREDUMP_HOSTNAME=",
+ [META_ARGV_DUMPABLE] = "COREDUMP_DUMPABLE=",
[META_COMM] = "COREDUMP_COMM=",
[META_EXE] = "COREDUMP_EXE=",
[META_UNIT] = "COREDUMP_UNIT=",
@@ -146,6 +148,7 @@ typedef struct Context {
PidRef pidref;
uid_t uid;
gid_t gid;
+ unsigned dumpable;
int signo;
uint64_t rlimit;
bool is_pid1;
@@ -433,14 +436,16 @@ static int grant_user_access(int core_fd, const Context *context) {
if (r < 0)
return r;
- /* We allow access if we got all the data and at_secure is not set and
- * the uid/gid matches euid/egid. */
+ /* We allow access if dumpable on the command line was exactly 1, we got all the data,
+ * at_secure is not set, and the uid/gid match euid/egid. */
bool ret =
+ context->dumpable == 1 &&
at_secure == 0 &&
uid != UID_INVALID && euid != UID_INVALID && uid == euid &&
gid != GID_INVALID && egid != GID_INVALID && gid == egid;
- log_debug("Will %s access (uid="UID_FMT " euid="UID_FMT " gid="GID_FMT " egid="GID_FMT " at_secure=%s)",
+ log_debug("Will %s access (dumpable=%u uid="UID_FMT " euid="UID_FMT " gid="GID_FMT " egid="GID_FMT " at_secure=%s)",
ret ? "permit" : "restrict",
+ context->dumpable,
uid, euid, gid, egid, yes_no(at_secure));
return ret;
}
@@ -1083,6 +1088,16 @@ static int context_parse_iovw(Context *context, struct iovec_wrapper *iovw) {
if (r < 0)
log_warning_errno(r, "Failed to parse resource limit \"%s\", ignoring: %m", context->meta[META_ARGV_RLIMIT]);
+ /* The value is set to contents of /proc/sys/fs/suid_dumpable, which we set to 2,
+ * if the process is marked as not dumpable, see PR_SET_DUMPABLE(2const). */
+ if (context->meta[META_ARGV_DUMPABLE]) {
+ r = safe_atou(context->meta[META_ARGV_DUMPABLE], &context->dumpable);
+ if (r < 0)
+ return log_error_errno(r, "Failed to parse dumpable field \"%s\": %m", context->meta[META_ARGV_DUMPABLE]);
+ if (context->dumpable > 2)
+ log_notice("Got unexpected %%d/dumpable value %u.", context->dumpable);
+ }
+
unit = context->meta[META_UNIT];
context->is_pid1 = streq(context->meta[META_ARGV_PID], "1") || streq_ptr(unit, SPECIAL_INIT_SCOPE);
context->is_journald = streq_ptr(unit, SPECIAL_JOURNALD_SERVICE);
diff --git a/sysctl.d/50-coredump.conf.in b/sysctl.d/50-coredump.conf.in
index 90c080bdfe..a550c87258 100644
--- a/sysctl.d/50-coredump.conf.in
+++ b/sysctl.d/50-coredump.conf.in
@@ -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
diff --git a/test/units/TEST-87-AUX-UTILS-VM.coredump.sh b/test/units/TEST-87-AUX-UTILS-VM.coredump.sh
index a170223f37..0d7bed5609 100755
--- a/test/units/TEST-87-AUX-UTILS-VM.coredump.sh
+++ b/test/units/TEST-87-AUX-UTILS-VM.coredump.sh
@@ -196,12 +196,17 @@ journalctl -b -n 1 --output=export --output-fields=MESSAGE,COREDUMP COREDUMP_EXE
/usr/lib/systemd/systemd-coredump --backtrace $$ 0 0 6 1679509900 12345
journalctl -b -n 1 --output=export --output-fields=MESSAGE,COREDUMP COREDUMP_EXE="/usr/bin/test-dump" |
/usr/lib/systemd/systemd-coredump --backtrace $$ 0 0 6 1679509901 12345 mymachine
+journalctl -b -n 1 --output=export --output-fields=MESSAGE,COREDUMP COREDUMP_EXE="/usr/bin/test-dump" |
+ /usr/lib/systemd/systemd-coredump --backtrace $$ 0 0 6 1679509902 12345 youmachine 1
# Wait a bit for the coredumps to get processed
timeout 30 bash -c "while [[ \$(coredumpctl list -q --no-legend $$ | wc -l) -lt 2 ]]; do sleep 1; done"
coredumpctl info $$
coredumpctl info COREDUMP_TIMESTAMP=1679509900000000
coredumpctl info COREDUMP_TIMESTAMP=1679509901000000
coredumpctl info COREDUMP_HOSTNAME="mymachine"
+coredumpctl info COREDUMP_TIMESTAMP=1679509902000000
+coredumpctl info COREDUMP_HOSTNAME="youmachine"
+coredumpctl info COREDUMP_DUMPABLE="1"
# This used to cause a stack overflow
systemd-run -t --property CoredumpFilter=all ls /tmp
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