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Add root group writeable flag to log file

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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.
This commit is contained in:
Petr Menšík
2022-01-10 12:34:42 +01:00
committed by Simon Kelley
parent c2f129ba3d
commit 1f8f78a49b
1 changed files with 18 additions and 5 deletions
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19
src/log.c
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@@ -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, /* If we're running as root and going to change uid later,
change the ownership here so that the file is always owned by change the ownership here so that the file is always owned by
the dnsmasq user. Then logrotate can just copy the owner. the dnsmasq user. Then logrotate can just copy the owner.
Failure of the chown call is OK, (for instance when started as non-root) */ 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) 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; ret = errno;
}
return ret; return ret;
} }