From patchwork Wed May 21 07:56:04 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 112742 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id AC5A1385843D for ; Wed, 21 May 2025 07:56:49 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org AC5A1385843D Authentication-Results: sourceware.org; dkim=pass (1024-bit key, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=QXv6r07d X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTP id 4446B3858C62 for ; Wed, 21 May 2025 07:56:11 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 4446B3858C62 Authentication-Results: sourceware.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 4446B3858C62 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1747814171; cv=none; b=oJSUSa5ICrDZfL+bDQ7JT1PgxqkaF9Z1yR2IEDJhxuNSKislmufTLH8XhwmH3Ny0uVF6eshFMnFXuBqC9rf27TqyfGSJebWx+2RofXXJQ7gjqjIhnF5n7Kjif7rmZ7SfnPN3TvfPiK6bmOg3ZOF3x2wLIbaRCn8T1ThyIjl4n1A= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1747814171; c=relaxed/simple; bh=uS/LFKibuMklhQgYDnu9jk6Kuc8ZYYPBYne14JICqt8=; h=DKIM-Signature:From:To:Subject:Date:Message-ID:MIME-Version; b=tlF6+tVayU9p7d2FhTewwzhf0M8gH0tZBvtQ5Br7/Bu5XqFAwiMbZp/8AKOi5mbCUH+o8wrVLOW3mOwiJgEFVXeH6TnQtb5+cjw2P/uMzYarurFmec7HL+GpiBUipdyG6WMXEqd2VQTXxV4anmdOTxLDUEtzn252MWJFvfqBSzY= ARC-Authentication-Results: i=1; server2.sourceware.org DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 4446B3858C62 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747814171; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type; bh=SDBn9OJliXxnA1jmr3OJENJnIZsXkltZgoH/TG0sbYQ=; b=QXv6r07dlkD1dcZk217TPiscaSd5ITClW9Q5tUlUqzcalwixdyo80B1N9Z29l1Spu9sfSk Jkx/pMLJSsIwfyc+8uZuLy5PeoCn4VyGLDkUMRmTWN4/WQNdMRMejtphS6jJx+Igckdue4 3immNvprZsisgZ7DIeHyc8rFWKggbUw= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-602-hr_76CrSOaGQPZzHZia_yQ-1; Wed, 21 May 2025 03:56:09 -0400 X-MC-Unique: hr_76CrSOaGQPZzHZia_yQ-1 X-Mimecast-MFC-AGG-ID: hr_76CrSOaGQPZzHZia_yQ_1747814168 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AF0BA180034A for ; Wed, 21 May 2025 07:56:08 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.45.224.17]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DF89619560A3 for ; Wed, 21 May 2025 07:56:07 +0000 (UTC) From: Florian Weimer To: libc-alpha@sourceware.org Subject: [PATCH] support: Pick group in support_capture_subprogram_self_sgid if UID == 0 Date: Wed, 21 May 2025 09:56:04 +0200 Message-ID: <87plg24ctn.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 7_2cKqwOrcWljHKbbiUjm_zWYfDswDANH51k0072jTA_1747814168 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-10.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_NUMSUBJECT, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H5, RCVD_IN_MSPIKE_WL, RCVD_IN_VALIDITY_RPBL_BLOCKED, RCVD_IN_VALIDITY_SAFE_BLOCKED, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces~patchwork=sourceware.org@sourceware.org When running as root, it is likely that we can run under any group. Pick a harmless group from /etc/group in this case. Reviewed-by: Carlos O'Donell --- support/support_capture_subprocess.c | 58 +++++++++++++++++++++++++++++++++--- 1 file changed, 54 insertions(+), 4 deletions(-) base-commit: 35fc356fa3b4f485bd3ba3114c9f774e5df7d3c2 diff --git a/support/support_capture_subprocess.c b/support/support_capture_subprocess.c index d99aafd370..9d88d6291a 100644 --- a/support/support_capture_subprocess.c +++ b/support/support_capture_subprocess.c @@ -21,7 +21,11 @@ #include #include +#include +#include +#include #include +#include #include #include #include @@ -210,10 +214,48 @@ err: return status; } +/* Returns true if a group with NAME has been found, and writes its + GID to *TARGET. */ +static bool +find_sgid_group (gid_t *target, const char *name) +{ + /* Do not use getgrname_r because it does not work in statically + linked binaries if the system libc is different. */ + FILE *fp = fopen ("/etc/group", "rce"); + if (fp == NULL) + return false; + __fsetlocking (fp, FSETLOCKING_BYCALLER); + + bool ok = false; + struct scratch_buffer buf; + scratch_buffer_init (&buf); + while (true) + { + struct group grp; + struct group *result = NULL; + int status = fgetgrent_r (fp, &grp, buf.data, buf.length, &result); + if (status == 0 && result != NULL) + { + if (strcmp (result->gr_name, name) == 0) + { + *target = result->gr_gid; + ok = true; + break; + } + } + else if (errno != ERANGE) + break; + else if (!scratch_buffer_grow (&buf)) + break; + } + scratch_buffer_free (&buf); + fclose (fp); + return ok; +} + int support_capture_subprogram_self_sgid (const char *child_id) { - gid_t target = 0; const int count = 64; gid_t groups[count]; @@ -225,6 +267,7 @@ support_capture_subprogram_self_sgid (const char *child_id) (intmax_t) getuid ()); gid_t current = getgid (); + gid_t target = current; for (int i = 0; i < ret; ++i) { if (groups[i] != current) @@ -234,9 +277,16 @@ support_capture_subprogram_self_sgid (const char *child_id) } } - if (target == 0) - FAIL_UNSUPPORTED("Could not find a suitable GID for user %jd\n", - (intmax_t) getuid ()); + if (target == current) + { + /* If running as root, try to find a harmless group for SGID. */ + if (getuid () != 0 + || (!find_sgid_group (&target, "nogroup") + && !find_sgid_group (&target, "bin") + && !find_sgid_group (&target, "daemon"))) + FAIL_UNSUPPORTED("Could not find a suitable GID for user %jd\n", + (intmax_t) getuid ()); + } return copy_and_spawn_sgid (child_id, target); }