| Message ID | 877ergqsmd.fsf@notabene.neil.brown.name (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Feb 14, 2018 at 12:15:06PM +1100, NeilBrown wrote: > > The interface for flushing the sunrpc auth cache was poorly > designed and has caused problems a number of times. > > The design is that you write a timestamp, and all entries > created before that time are discarded. > The most obvious problem is that this is not what people > actually want. They want to just flush the whole cache. > The 1-second granularity can be a problem, as can the use > of wall-clock time. > > A current problem is that code will write the current time to > this file - expecting it to clear everything - and if the > seconds number ticks over before this timestamp is checked, > the test "then >= now" fails, and a full flush isn't forced. > > So lets just drop the subtleties and always flush the whole > cache. The worst this could do is impose an extra cost > refilling it, but that would require someone to be using > non-standard tools. > > We still report an error if the string written is not a number, > but we cause any valid number to flush the whole cache. Thanks, applying for 4.17 (unless someone thinks it's more urgent). --b. > > Reported-by: "Wang, Alan 1. (NSB - CN/Hangzhou)" <alan.1.wang@nokia-sbell.com> > Signed-off-by: NeilBrown <neilb@suse.com> > --- > net/sunrpc/cache.c | 32 ++++++++++++++++---------------- > 1 file changed, 16 insertions(+), 16 deletions(-) > > diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c > index 8a7e1c774f9c..26582e27be6a 100644 > --- a/net/sunrpc/cache.c > +++ b/net/sunrpc/cache.c > @@ -1450,8 +1450,8 @@ static ssize_t write_flush(struct file *file, const char __user *buf, > struct cache_detail *cd) > { > char tbuf[20]; > - char *bp, *ep; > - time_t then, now; > + char *ep; > + time_t now; > > if (*ppos || count > sizeof(tbuf)-1) > return -EINVAL; > @@ -1461,24 +1461,24 @@ static ssize_t write_flush(struct file *file, const char __user *buf, > simple_strtoul(tbuf, &ep, 0); > if (*ep && *ep != '\n') > return -EINVAL; > + /* Note that while we check that 'buf' holds a valid number, > + * we always ignore the value and just flush everything. > + * Making use of the number leads to races. > + */ > > - bp = tbuf; > - then = get_expiry(&bp); > now = seconds_since_boot(); > - cd->nextcheck = now; > - /* Can only set flush_time to 1 second beyond "now", or > - * possibly 1 second beyond flushtime. This is because > - * flush_time never goes backwards so it mustn't get too far > - * ahead of time. > + /* Always flush everything, so behave like cache_purge() > + * Do this by advancing flush_time to the current time, > + * or by one second if it has already reached the current time. > + * Newly added cache entries will always have ->last_refresh greater > + * that ->flush_time, so they don't get flushed prematurely. > */ > - if (then >= now) { > - /* Want to flush everything, so behave like cache_purge() */ > - if (cd->flush_time >= now) > - now = cd->flush_time + 1; > - then = now; > - } > > - cd->flush_time = then; > + if (cd->flush_time >= now) > + now = cd->flush_time + 1; > + > + cd->flush_time = now; > + cd->nextcheck = now; > cache_flush(); > > *ppos += count; > -- > 2.14.0.rc0.dirty > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c index 8a7e1c774f9c..26582e27be6a 100644 --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -1450,8 +1450,8 @@ static ssize_t write_flush(struct file *file, const char __user *buf, struct cache_detail *cd) { char tbuf[20]; - char *bp, *ep; - time_t then, now; + char *ep; + time_t now; if (*ppos || count > sizeof(tbuf)-1) return -EINVAL; @@ -1461,24 +1461,24 @@ static ssize_t write_flush(struct file *file, const char __user *buf, simple_strtoul(tbuf, &ep, 0); if (*ep && *ep != '\n') return -EINVAL; + /* Note that while we check that 'buf' holds a valid number, + * we always ignore the value and just flush everything. + * Making use of the number leads to races. + */ - bp = tbuf; - then = get_expiry(&bp); now = seconds_since_boot(); - cd->nextcheck = now; - /* Can only set flush_time to 1 second beyond "now", or - * possibly 1 second beyond flushtime. This is because - * flush_time never goes backwards so it mustn't get too far - * ahead of time. + /* Always flush everything, so behave like cache_purge() + * Do this by advancing flush_time to the current time, + * or by one second if it has already reached the current time. + * Newly added cache entries will always have ->last_refresh greater + * that ->flush_time, so they don't get flushed prematurely. */ - if (then >= now) { - /* Want to flush everything, so behave like cache_purge() */ - if (cd->flush_time >= now) - now = cd->flush_time + 1; - then = now; - } - cd->flush_time = then; + if (cd->flush_time >= now) + now = cd->flush_time + 1; + + cd->flush_time = now; + cd->nextcheck = now; cache_flush(); *ppos += count;
The interface for flushing the sunrpc auth cache was poorly designed and has caused problems a number of times. The design is that you write a timestamp, and all entries created before that time are discarded. The most obvious problem is that this is not what people actually want. They want to just flush the whole cache. The 1-second granularity can be a problem, as can the use of wall-clock time. A current problem is that code will write the current time to this file - expecting it to clear everything - and if the seconds number ticks over before this timestamp is checked, the test "then >= now" fails, and a full flush isn't forced. So lets just drop the subtleties and always flush the whole cache. The worst this could do is impose an extra cost refilling it, but that would require someone to be using non-standard tools. We still report an error if the string written is not a number, but we cause any valid number to flush the whole cache. Reported-by: "Wang, Alan 1. (NSB - CN/Hangzhou)" <alan.1.wang@nokia-sbell.com> Signed-off-by: NeilBrown <neilb@suse.com> --- net/sunrpc/cache.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-)