[Dnsmasq-discuss] [PATCH] Preserve existing log file permissions when adding group-write bit.

[Simon Kelley]

Patch applied.


Cheers,

Simon.


On 21/04/2026 10:00, Florian Margaine via Dnsmasq-discuss wrote:
> Hi,
> 
> Commit 1f8f78a49b8fd ("Add root group writeable flag to log file")
> introduced a fchmod() call in log_start() that resets the file mode
> to a hardcoded value (0660), discarding any pre-existing permissions.
> This broke our usage of dnsmasq where we create the log file with
> specific permissions before starting dnsmasq in an LXC container
> namespace, so that unprivileged users inside the container can read
> the log. The hardcoded mode strips those permissions on startup.
> 
> Use the existing stat result to OR in S_IWGRP instead, equivalent
> to chmod g+w, so that only the group-write bit is added without
> disturbing other permission bits.
> 
> Co-Authored-By: Claude Opus 4.6 <noreply at anthropic.com>
> ---
>   src/log.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/log.c b/src/log.c
> index c8e8348..131e580 100644
> --- a/src/log.c
> +++ b/src/log.c
> @@ -113,7 +113,7 @@ int log_start(struct passwd *ent_pw, int errfd)
>         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);
> + (void)fchmod(log_fd, ls.st_mode | S_IWGRP);
>         if (fchown(log_fd, ent_pw->pw_uid, -1) != 0)
>    ret = errno;
>       }
> --
> 2.47.3
> 
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