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a673ceed38
systemd/1280-coredump-use-d-in-kernel-core-pattern.patch
Jan Macku a673ceed38 systemd-252-60 
Resolves: RHEL-115182,RHEL-97175,RHEL-107268
2025-11-05 09:44:11 +01:00

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From fbc5015c95298c71c806b5e80207e52688aad69a 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>
In principle, %d might return a value other than 0, 1, or 2 in the future.
Thus, we accept those, but emit a notice.
(cherry picked from commit 0c49e0049b7665bb7769a13ef346fef92e1ad4d6)
Related: RHEL-104138
---
man/systemd-coredump.xml | 10 ++++++++++
src/coredump/coredump.c | 22 +++++++++++++++++++---
sysctl.d/50-coredump.conf.in | 2 +-
test/units/testsuite-74.coredump.sh | 5 +++++
4 files changed, 35 insertions(+), 4 deletions(-)
diff --git a/man/systemd-coredump.xml b/man/systemd-coredump.xml
index cb9f47745b..6cfa04f466 100644
--- a/man/systemd-coredump.xml
+++ b/man/systemd-coredump.xml
@@ -259,6 +259,16 @@ 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>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term><varname>COREDUMP_OPEN_FDS=</varname></term>
diff --git a/src/coredump/coredump.c b/src/coredump/coredump.c
index 458857ffb2..cd10678c43 100644
--- a/src/coredump/coredump.c
+++ b/src/coredump/coredump.c
@@ -97,7 +97,9 @@ 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 */
_META_ARGV_MAX,
+
/* If new fields are added, they should be added here, to maintain compatibility
* with callers which don't know about the new fields. */
@@ -126,6 +128,7 @@ 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=",
@@ -138,6 +141,7 @@ typedef struct Context {
pid_t pid;
uid_t uid;
gid_t gid;
+ unsigned dumpable;
bool is_pid1;
bool is_journald;
} Context;
@@ -453,14 +457,16 @@ 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 %d/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;
}
@@ -1089,6 +1095,16 @@ static int save_context(Context *context, const struct iovec_wrapper *iovw) {
return log_error_errno(r, "Failed to parse GID \"%s\": %m", context->meta[META_ARGV_GID]);
+ /* 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 5fb551a8cf..9c10a89828 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=|{{ROOTLIBEXECDIR}}/systemd-coredump %P %u %g %s %t %c %h
+kernel.core_pattern=|{{ROOTLIBEXECDIR}}/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/testsuite-74.coredump.sh b/test/units/testsuite-74.coredump.sh
index 0163131096..b72313672c 100755
--- a/test/units/testsuite-74.coredump.sh
+++ b/test/units/testsuite-74.coredump.sh
@@ -225,12 +225,17 @@ 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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