From e342e4d5c3093d8dd9e2d622e46d36f67bfb4925 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Petr=20Men=C5=A1=C3=ADk?= Date: Mon, 10 Jan 2022 12:34:42 +0100 Subject: [PATCH] Add root group writeable flag to log file Some systems strips even root process capability of writing to different users file. That include systemd under Fedora. When log-facility=/var/log/dnsmasq.log is used, log file with mode 0640 is created. But restart then fails, because such log file can be used only when created new. Existing file cannot be opened by root when starting, causing fatal error. Avoid that by adding root group writeable flag. Ensure group is always root when granting write access. If it is anything else, administrator has to configure correct rights. (cherry picked from commit 1f8f78a49b8fd6b2862a3882053b1c6e6e111e5c) --- src/log.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/src/log.c b/src/log.c index 1ec3447..bcd6e52 100644 --- a/src/log.c +++ b/src/log.c @@ -100,10 +100,23 @@ int log_start(struct passwd *ent_pw, int errfd) /* If we're running as root and going to change uid later, change the ownership here so that the file is always owned by the dnsmasq user. Then logrotate can just copy the owner. - Failure of the chown call is OK, (for instance when started as non-root) */ - if (log_to_file && !log_stderr && ent_pw && ent_pw->pw_uid != 0 && - fchown(log_fd, ent_pw->pw_uid, -1) != 0) - ret = errno; + Failure of the chown call is OK, (for instance when started as non-root). + + If we've created a file with group-id root, we also make + the file group-writable. This gives processes in the root group + write access to the file and avoids the problem that on some systems, + once the file is owned by the dnsmasq user, it can't be written + whilst dnsmasq is running as root during startup. + */ + if (log_to_file && !log_stderr && ent_pw && ent_pw->pw_uid != 0) + { + struct stat ls; + if (getgid() == 0 && fstat(log_fd, &ls) == 0 && ls.st_gid == 0 && + (ls.st_mode & S_IWGRP) == 0) + (void)fchmod(log_fd, S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP); + if (fchown(log_fd, ent_pw->pw_uid, -1) != 0) + ret = errno; + } return ret; } @@ -118,7 +131,7 @@ int log_reopen(char *log_file) /* NOTE: umask is set to 022 by the time this gets called */ if (log_file) - log_fd = open(log_file, O_WRONLY|O_CREAT|O_APPEND, S_IRUSR|S_IWUSR|S_IRGRP); + log_fd = open(log_file, O_WRONLY|O_CREAT|O_APPEND, S_IRUSR|S_IWUSR|S_IRGRP); else { #if defined(HAVE_SOLARIS_NETWORK) || defined(__ANDROID__) -- 2.40.1