From: Zbigniew Jędrzejewski-Szmek Date: Tue, 29 Apr 2025 12:47:59 +0000 (+0200) Subject: coredump: use %d in kernel core pattern X-Git-Tag: v258-rc1~448^2~6 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0c49e0049b7665bb7769a13ef346fef92e1ad4d6;p=thirdparty%2Fsystemd.git 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 In principle, %d might return a value other than 0, 1, or 2 in the future. Thus, we accept those, but emit a notice. --- diff --git a/man/systemd-coredump.xml b/man/systemd-coredump.xml index 9972ba02e4d..b62eb7b1296 100644 --- a/man/systemd-coredump.xml +++ b/man/systemd-coredump.xml @@ -329,6 +329,18 @@ COREDUMP_FILENAME=/var/lib/systemd/coredump/core.Web….552351.….zst + + COREDUMP_DUMPABLE= + + The PR_GET_DUMPABLE field as reported by the kernel, see + prctl2. + + + + + + COREDUMP_OPEN_FDS= diff --git a/src/coredump/coredump.c b/src/coredump/coredump.c index 4bc1e4ad806..bfb7db9d284 100644 --- a/src/coredump/coredump.c +++ b/src/coredump/coredump.c @@ -103,6 +103,7 @@ 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, @@ -131,6 +132,7 @@ 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=", @@ -141,6 +143,7 @@ typedef struct Context { PidRef pidref; uid_t uid; gid_t gid; + unsigned dumpable; int signo; uint64_t rlimit; bool is_pid1; @@ -437,14 +440,16 @@ 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; } @@ -1087,6 +1092,16 @@ 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 90c080bdfef..a550c87258f 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 6ad7e29e28a..ce4a2c9ed15 100755 --- a/test/units/TEST-87-AUX-UTILS-VM.coredump.sh +++ b/test/units/TEST-87-AUX-UTILS-VM.coredump.sh @@ -198,12 +198,17 @@ 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