coredump: use %d in kernel core pattern

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 0c49e0049b7665bb7769a13ef346fef92e1ad4d6)
(cherry-picked from c58a8a6ec9817275bb4babaa2c08e0e35090d4e3)

diff --git a/man/systemd-coredump.xml b/man/systemd-coredump.xml
index 737b80de9ae181cd0b76570b48a6c8e1867a7efe..0f5ccf12f9baf7f137fff0cfb0c2c513f1a49cf7 100644 (file)
--- 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 d200681b2a1b2ba43744d0aa9cd2ce9daf917f33..bb1c6ec3833f3f352c6d6cdf6146ee7d47e83f72 100644 (file)
--- a/src/coredump/coredump.c
+++ b/src/coredump/coredump.c
@@ -98,6 +98,7 @@ 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,
@@ -126,6 +127,7 @@ 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 +140,7 @@ typedef struct Context {
         pid_t pid;
         uid_t uid;
         gid_t gid;
+        unsigned dumpable;
         bool is_pid1;
         bool is_journald;
 } Context;
@@ -396,14 +399,16 @@ 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;
 }
@@ -993,6 +998,16 @@ static int save_context(Context *context, const struct iovec_wrapper *iovw) {
         if (r < 0)
                 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 90c080bdfefafd1a28eb29d3a616fe207b1ea9bf..a550c87258f6b84153101d6730a581674467de57 100644 (file)
--- 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-74-AUX-UTILS.coredump.sh b/test/units/TEST-74-AUX-UTILS.coredump.sh
index 01d6a860d5409e1c4f76424f95d7a0bb9a386ae7..902a19d727308274466b27f8712940b0e8e14c83 100755 (executable)
--- a/test/units/TEST-74-AUX-UTILS.coredump.sh
+++ b/test/units/TEST-74-AUX-UTILS.coredump.sh
@@ -199,12 +199,17 @@ 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