From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: libc-alpha@sourceware.org
Subject: Re: [PATCH 5/5] resolv: Fix ABA race in /etc/resolv.conf change detection [BZ #25420]
Date: Thu, 13 Feb 2020 21:59:00 -0000 [thread overview]
Message-ID: <0728f253-b851-d9d5-7c9b-a1a514600afc@linaro.org> (raw)
In-Reply-To: <95b81fd1ccd9d41c4f6a897a1c43d1298da0486e.1579631655.git.fweimer@redhat.com>
On 21/01/2020 15:42, Florian Weimer wrote:
> __resolv_conf_get_current should only record the initial file
> change data if after verifying that file just read matches the
> original measurement. Fixes commit aef16cc8a4c670036d45590877
> ("resolv: Automatically reload a changed /etc/resolv.conf file
> [BZ #984]").
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> resolv/resolv_conf.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/resolv/resolv_conf.c b/resolv/resolv_conf.c
> index bdd2ebb909..29a1f4fb94 100644
> --- a/resolv/resolv_conf.c
> +++ b/resolv/resolv_conf.c
> @@ -136,18 +136,25 @@ __resolv_conf_get_current (void)
> {
> /* Parse configuration while holding the lock. This avoids
> duplicate work. */
> - conf = __resolv_conf_load (NULL, NULL);
> + struct file_change_detection after_load;
> + conf = __resolv_conf_load (NULL, &after_load);
> if (conf != NULL)
> {
> if (global_copy->conf_current != NULL)
> conf_decrement (global_copy->conf_current);
> global_copy->conf_current = conf; /* Takes ownership. */
>
> - /* Update file modification stamps. The configuration we
> - read could be a newer version of the file, but this does
> - not matter because this will lead to an extraneous reload
> - later. */
> - global_copy->file_resolve_conf = initial;
> + /* Update file change detection data, but only if it matches
> + the initial measurement. This avoids an ABA race in case
> + /etc/resolv.conf is temporarily replaced while the file
> + is read (after the initial measurement), and restored to
> + the initial version later. */
> + if (file_is_unchanged (&initial, &after_load))
> + global_copy->file_resolve_conf = after_load;
> + else
> + /* If there is a discrepancy, trigger a reload during the
> + next use. */
> + global_copy->file_resolve_conf.size = -1;
> }
> }
>
>
Ok.
prev parent reply other threads:[~2020-02-13 21:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-21 18:41 [PATCH 0/5] Race condition in /etc/resolv.conf reloading (bug 25420) Florian Weimer
2020-01-21 18:41 ` [PATCH 1/5] Add internal <file_change_detection.h> header file Florian Weimer
2020-02-10 19:47 ` Adhemerval Zanella
2020-02-10 19:58 ` Florian Weimer
2020-02-10 20:57 ` Adhemerval Zanella
2020-01-21 18:42 ` [PATCH 2/5] resolv: Use <file_change_detection.h> in __resolv_conf_get_current Florian Weimer
2020-02-13 20:53 ` Adhemerval Zanella
2020-01-21 18:42 ` [PATCH 3/5] resolv: Fix file handle leak in __resolv_conf_load [BZ #25429] Florian Weimer
2020-02-13 21:01 ` Adhemerval Zanella
2020-02-13 21:08 ` Florian Weimer
2020-02-13 21:30 ` Adhemerval Zanella
2020-01-21 18:42 ` [PATCH 4/5] resolv: Enhance __resolv_conf_load to capture file change data Florian Weimer
2020-02-13 21:33 ` Adhemerval Zanella
2020-01-21 21:28 ` [PATCH 5/5] resolv: Fix ABA race in /etc/resolv.conf change detection [BZ #25420] Florian Weimer
2020-02-13 21:59 ` Adhemerval Zanella [this message]
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