shadow-utils/shadow-4.9-skip-over-reserved-ids.patch

From baae5b4a06c905d9f52ed1f922a0d7d0625d11cf Mon Sep 17 00:00:00 2001
From: Martin Kletzander <nert.pinx@gmail.com>
Date: Wed, 1 Feb 2023 15:36:41 +0100
Subject: [PATCH] find_new_[gu]id(): Skip over IDs that are reserved for legacy
 reasons

Some programs don't support `(uint16_t) -1` or `(uint32_t) -1` as user
or group IDs.  This is because `-1` is used as an error code or as an
unspecified ID, e.g. in `chown(2)` parameters, and in the past, `gid_t`
and `uid_t` have changed width.  For legacy reasons, those values have
been kept reserved in programs today (for example systemd does this; see
the documentation in the link below).

This should not be confused with catching overflow in the ID values,
since that is already caught by our ERANGE checks.  This is about not
using reserved values that have been reserved for legacy reasons.

Link: <https://systemd.io/UIDS-GIDS/>
Reviewed-by: Alejandro Colomar <alx@kernel.org>
Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
---
 libmisc/find_new_gid.c | 38 ++++++++++++++++++++++++++++----------
 libmisc/find_new_uid.c | 38 ++++++++++++++++++++++++++++----------
 2 files changed, 56 insertions(+), 20 deletions(-)

diff --git a/libmisc/find_new_gid.c b/libmisc/find_new_gid.c
index 70ba95a2..da1d8d55 100644
--- a/libmisc/find_new_gid.c
+++ b/libmisc/find_new_gid.c
@@ -98,6 +98,7 @@ static int get_ranges (bool sys_group, gid_t *min_id, gid_t *max_id,
  *
  * On success, return 0
  * If the ID is in use, return EEXIST
+ * If the ID might clash with -1, return EINVAL
  * If the ID is outside the range, return ERANGE
  * In other cases, return errno from getgrgid()
  */
@@ -111,6 +112,11 @@ static int check_gid (const gid_t gid,
 		return ERANGE;
 	}
 
+	/* Check for compatibility with 16b and 32b gid_t error codes */
+	if (gid == UINT16_MAX || gid == UINT32_MAX) {
+		return EINVAL;
+	}
+
 	/*
 	 * Check whether we already detected this GID
 	 * using the gr_next() loop
@@ -182,10 +188,10 @@ int find_new_gid (bool sys_group,
 			 * gr_locate_gid() found the GID in an as-yet uncommitted
 			 * entry. We'll proceed below and auto-set a GID.
 			 */
-		} else if (result == EEXIST || result == ERANGE) {
+		} else if (result == EEXIST || result == ERANGE || result == EINVAL) {
 			/*
 			 * Continue on below. At this time, we won't
-			 * treat these two cases differently.
+			 * treat these three cases differently.
 			 */
 		} else {
 			/*
@@ -296,8 +302,11 @@ int find_new_gid (bool sys_group,
 				*gid = id;
 				free (used_gids);
 				return 0;
-			} else if (result == EEXIST) {
-				/* This GID is in use, we'll continue to the next */
+			} else if (result == EEXIST || result == EINVAL) {
+				/*
+				 * This GID is in use or unusable, we'll
+				 * continue to the next.
+				 */
 			} else {
 				/*
 				 * An unexpected error occurred.
@@ -339,8 +348,11 @@ int find_new_gid (bool sys_group,
 					*gid = id;
 					free (used_gids);
 					return 0;
-				} else if (result == EEXIST) {
-					/* This GID is in use, we'll continue to the next */
+				} else if (result == EEXIST || result == EINVAL) {
+					/*
+					 * This GID is in use or unusable, we'll
+					 * continue to the next.
+					 */
 				} else {
 					/*
 					 * An unexpected error occurred.
@@ -399,8 +411,11 @@ int find_new_gid (bool sys_group,
 				*gid = id;
 				free (used_gids);
 				return 0;
-			} else if (result == EEXIST) {
-				/* This GID is in use, we'll continue to the next */
+			} else if (result == EEXIST || result == EINVAL) {
+				/*
+				 * This GID is in use or unusable, we'll
+				 * continue to the next.
+				 */
 			} else {
 				/*
 				 * An unexpected error occurred.
@@ -442,8 +457,11 @@ int find_new_gid (bool sys_group,
 					*gid = id;
 					free (used_gids);
 					return 0;
-				} else if (result == EEXIST) {
-					/* This GID is in use, we'll continue to the next */
+				} else if (result == EEXIST || result == EINVAL) {
+					/*
+					 * This GID is in use or unusable, we'll
+					 * continue to the next.
+					 */
 				} else {
 					/*
 					 * An unexpected error occurred.
diff --git a/libmisc/find_new_uid.c b/libmisc/find_new_uid.c
index 6b71dfe5..09885236 100644
--- a/libmisc/find_new_uid.c
+++ b/libmisc/find_new_uid.c
@@ -98,6 +98,7 @@ static int get_ranges (bool sys_user, uid_t *min_id, uid_t *max_id,
  *
  * On success, return 0
  * If the ID is in use, return EEXIST
+ * If the ID might clash with -1, return EINVAL
  * If the ID is outside the range, return ERANGE
  * In other cases, return errno from getpwuid()
  */
@@ -111,6 +112,11 @@ static int check_uid(const uid_t uid,
 		return ERANGE;
 	}
 
+	/* Check for compatibility with 16b and 32b uid_t error codes */
+	if (uid == UINT16_MAX || uid == UINT32_MAX) {
+		return EINVAL;
+	}
+
 	/*
 	 * Check whether we already detected this UID
 	 * using the pw_next() loop
@@ -182,10 +188,10 @@ int find_new_uid(bool sys_user,
 			 * pw_locate_uid() found the UID in an as-yet uncommitted
 			 * entry. We'll proceed below and auto-set an UID.
 			 */
-		} else if (result == EEXIST || result == ERANGE) {
+		} else if (result == EEXIST || result == ERANGE || result == EINVAL) {
 			/*
 			 * Continue on below. At this time, we won't
-			 * treat these two cases differently.
+			 * treat these three cases differently.
 			 */
 		} else {
 			/*
@@ -296,8 +302,11 @@ int find_new_uid(bool sys_user,
 				*uid = id;
 				free (used_uids);
 				return 0;
-			} else if (result == EEXIST) {
-				/* This UID is in use, we'll continue to the next */
+			} else if (result == EEXIST || result == EINVAL) {
+				/*
+				 * This GID is in use or unusable, we'll
+				 * continue to the next.
+				 */
 			} else {
 				/*
 				 * An unexpected error occurred.
@@ -339,8 +348,11 @@ int find_new_uid(bool sys_user,
 					*uid = id;
 					free (used_uids);
 					return 0;
-				} else if (result == EEXIST) {
-					/* This UID is in use, we'll continue to the next */
+				} else if (result == EEXIST || result == EINVAL) {
+					/*
+					 * This GID is in use or unusable, we'll
+					 * continue to the next.
+					 */
 				} else {
 					/*
 					 * An unexpected error occurred.
@@ -399,8 +411,11 @@ int find_new_uid(bool sys_user,
 				*uid = id;
 				free (used_uids);
 				return 0;
-			} else if (result == EEXIST) {
-				/* This UID is in use, we'll continue to the next */
+			} else if (result == EEXIST || result == EINVAL) {
+				/*
+				 * This GID is in use or unusable, we'll
+				 * continue to the next.
+				 */
 			} else {
 				/*
 				 * An unexpected error occurred.
@@ -442,8 +457,11 @@ int find_new_uid(bool sys_user,
 					*uid = id;
 					free (used_uids);
 					return 0;
-				} else if (result == EEXIST) {
-					/* This UID is in use, we'll continue to the next */
+				} else if (result == EEXIST || result == EINVAL) {
+					/*
+					 * This GID is in use or unusable, we'll
+					 * continue to the next.
+					 */
 				} else {
 					/*
 					 * An unexpected error occurred.
-- 
2.40.1