File better_handle_failures_to_chown.patch of Package libteam.25992

From 44ed6a1724bac01cd1c1dd25defb62237df5f379 Mon Sep 17 00:00:00 2001
From: Thomas Haller <thaller@redhat.com>
Date: Fri, 21 May 2021 18:32:07 +0200
Subject: [PATCH 1/1] teamd: better handle failures to chown(TEAMD_RUN_DIR)
 during teamd_drop_privileges()

NetworkManager is exec-ing teamd while running without CAP_CHOWN.

When teamd is configured to drop privileges, then it will call chown
while still running as root user. But the command will fail because of
lack of CAP_CHOWN.

Note that chown() succeeds if the calling process has CAP_CHOWN or if
the file already is owned by the calling user/group (whereas, changing
the group will still work, if the user is a member of that group).

The directory might have already been prepared with the right user/group.
Let's handle that. If the first chown() as root succeeds, we are good.
If it fails, we will retry after changing the user id. If the directory
already has the right/compatible user, this command will succeeds too
and teamd can proceed.

See-also: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/722

Signed-off-by: Thomas Haller <thaller@redhat.com>
---
 teamd/teamd.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/teamd/teamd.c b/teamd/teamd.c
index b310140570c5..3ef3d6cf09f6 100644
--- a/teamd/teamd.c
+++ b/teamd/teamd.c
@@ -1714,6 +1714,7 @@ static int teamd_drop_privileges()
 	cap_t my_caps;
 	struct passwd *pw = NULL;
 	struct group *grpent = NULL;
+	int chown_succeeded;
 
 	if ((pw = getpwnam(TEAMD_USER)) == NULL) {
 		fprintf(stderr, "Error reading user %s entry (%m)\n", TEAMD_USER);
@@ -1734,11 +1735,12 @@ static int teamd_drop_privileges()
 		goto error;
 	}
 
-	if (chown(TEAMD_RUN_DIR, pw->pw_uid, pw->pw_gid) < 0) {
-		fprintf(stderr, "Unable to change ownership of %s to %s/%s (%m)\n",
-			TEAMD_RUN_DIR, TEAMD_USER, TEAMD_GROUP);
-		goto error;
-	}
+	/* Try to change owner while still being root. We might not have
+	 * capabilities, so this might fail. At this point, we accept that,
+	 * because the directory might have been prepared with a suitable owner
+	 * already. But on failure, we will retry as the new user below.
+	 */
+	chown_succeeded = (chown(TEAMD_RUN_DIR, pw->pw_uid, pw->pw_gid) == 0);
 
 	if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0)
 		goto error;
@@ -1758,6 +1760,12 @@ static int teamd_drop_privileges()
 		goto error;
 	}
 
+	if (!chown_succeeded && chown(TEAMD_RUN_DIR, pw->pw_uid, pw->pw_gid) < 0) {
+		fprintf(stderr, "Unable to change ownership of %s to %s/%s (%m)\n",
+			TEAMD_RUN_DIR, TEAMD_USER, TEAMD_GROUP);
+		goto error;
+	}
+
 	if ((my_caps = cap_init()) == NULL)
 		goto error;
 	if (cap_set_flag(my_caps, CAP_EFFECTIVE, ARRAY_SIZE(cv), cv, CAP_SET) < 0)
-- 
2.31.1