From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> To: Jason Gunthorpe <jgg@ziepe.ca> Cc: Leon Romanovsky <leon@kernel.org>, Peilin Ye <yepeilin.cs@gmail.com>, Santosh Shilimkar <santosh.shilimkar@oracle.com>, "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, Dan Carpenter <dan.carpenter@oracle.com>, Arnd Bergmann <arnd@arndb.de>, linux-kernel-mentees@lists.linuxfoundation.org, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org Subject: Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get() Date: Fri, 31 Jul 2020 16:21:48 +0200 [thread overview] Message-ID: <20200731142148.GA1718799@kroah.com> (raw) In-Reply-To: <20200731140452.GE24045@ziepe.ca> On Fri, Jul 31, 2020 at 11:04:52AM -0300, Jason Gunthorpe wrote: > On Fri, Jul 31, 2020 at 07:33:33AM +0200, Greg Kroah-Hartman wrote: > > On Fri, Jul 31, 2020 at 07:33:06AM +0200, Greg Kroah-Hartman wrote: > > > On Fri, Jul 31, 2020 at 07:53:01AM +0300, Leon Romanovsky wrote: > > > > On Thu, Jul 30, 2020 at 03:20:26PM -0400, Peilin Ye wrote: > > > > > rds_notify_queue_get() is potentially copying uninitialized kernel stack > > > > > memory to userspace since the compiler may leave a 4-byte hole at the end > > > > > of `cmsg`. > > > > > > > > > > In 2016 we tried to fix this issue by doing `= { 0 };` on `cmsg`, which > > > > > unfortunately does not always initialize that 4-byte hole. Fix it by using > > > > > memset() instead. > > > > > > > > Of course, this is the difference between "{ 0 }" and "{}" initializations. > > > > > > Really? Neither will handle structures with holes in it, try it and > > > see. > > > > And if true, where in the C spec does it say that? > > The spec was updated in C11 to require zero'ing padding when doing > partial initialization of aggregates (eg = {}) > > """if it is an aggregate, every member is initialized (recursively) > according to these rules, and any padding is initialized to zero > bits;""" But then why does the compilers not do this? > The difference between {0} and the {} extension is only that {} > reliably triggers partial initialization for all kinds of aggregates, > while {0} has a number of edge cases where it can fail to compile. > > IIRC gcc has cleared the padding during aggregate initialization for a > long time. Huh? Last we checked a few months ago, no, it did not do that. > Considering we have thousands of aggregate initializers it > seems likely to me Linux also requires a compiler with this C11 > behavior to operate correctly. Note that this is not an "operate correctly" thing, it is a "zero out stale data in structure paddings so that data will not leak to userspace" thing. > Does this patch actually fix anything? My compiler generates identical > assembly code in either case. What compiler version? thanks, greg k-h
WARNING: multiple messages have this Message-ID (diff)
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> To: Jason Gunthorpe <jgg@ziepe.ca> Cc: rds-devel@oss.oracle.com, Arnd Bergmann <arnd@arndb.de>, Leon Romanovsky <leon@kernel.org>, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, Santosh Shilimkar <santosh.shilimkar@oracle.com>, linux-kernel@vger.kernel.org, "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, linux-kernel-mentees@lists.linuxfoundation.org, Peilin Ye <yepeilin.cs@gmail.com>, Dan Carpenter <dan.carpenter@oracle.com> Subject: Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get() Date: Fri, 31 Jul 2020 16:21:48 +0200 [thread overview] Message-ID: <20200731142148.GA1718799@kroah.com> (raw) In-Reply-To: <20200731140452.GE24045@ziepe.ca> On Fri, Jul 31, 2020 at 11:04:52AM -0300, Jason Gunthorpe wrote: > On Fri, Jul 31, 2020 at 07:33:33AM +0200, Greg Kroah-Hartman wrote: > > On Fri, Jul 31, 2020 at 07:33:06AM +0200, Greg Kroah-Hartman wrote: > > > On Fri, Jul 31, 2020 at 07:53:01AM +0300, Leon Romanovsky wrote: > > > > On Thu, Jul 30, 2020 at 03:20:26PM -0400, Peilin Ye wrote: > > > > > rds_notify_queue_get() is potentially copying uninitialized kernel stack > > > > > memory to userspace since the compiler may leave a 4-byte hole at the end > > > > > of `cmsg`. > > > > > > > > > > In 2016 we tried to fix this issue by doing `= { 0 };` on `cmsg`, which > > > > > unfortunately does not always initialize that 4-byte hole. Fix it by using > > > > > memset() instead. > > > > > > > > Of course, this is the difference between "{ 0 }" and "{}" initializations. > > > > > > Really? Neither will handle structures with holes in it, try it and > > > see. > > > > And if true, where in the C spec does it say that? > > The spec was updated in C11 to require zero'ing padding when doing > partial initialization of aggregates (eg = {}) > > """if it is an aggregate, every member is initialized (recursively) > according to these rules, and any padding is initialized to zero > bits;""" But then why does the compilers not do this? > The difference between {0} and the {} extension is only that {} > reliably triggers partial initialization for all kinds of aggregates, > while {0} has a number of edge cases where it can fail to compile. > > IIRC gcc has cleared the padding during aggregate initialization for a > long time. Huh? Last we checked a few months ago, no, it did not do that. > Considering we have thousands of aggregate initializers it > seems likely to me Linux also requires a compiler with this C11 > behavior to operate correctly. Note that this is not an "operate correctly" thing, it is a "zero out stale data in structure paddings so that data will not leak to userspace" thing. > Does this patch actually fix anything? My compiler generates identical > assembly code in either case. What compiler version? thanks, greg k-h _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees
next prev parent reply other threads:[~2020-07-31 14:22 UTC|newest] Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-30 19:20 [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get() Peilin Ye 2020-07-30 19:20 ` Peilin Ye 2020-07-30 19:29 ` santosh.shilimkar 2020-07-30 19:29 ` santosh.shilimkar 2020-07-31 4:53 ` Leon Romanovsky 2020-07-31 4:53 ` Leon Romanovsky 2020-07-31 5:33 ` Greg Kroah-Hartman 2020-07-31 5:33 ` Greg Kroah-Hartman 2020-07-31 5:33 ` Greg Kroah-Hartman 2020-07-31 5:33 ` Greg Kroah-Hartman 2020-07-31 6:29 ` Andy Shevchenko 2020-07-31 7:00 ` Leon Romanovsky 2020-07-31 7:00 ` Leon Romanovsky 2020-07-31 7:05 ` Andy Shevchenko 2020-07-31 7:05 ` Andy Shevchenko 2020-07-31 14:04 ` Jason Gunthorpe 2020-07-31 14:04 ` Jason Gunthorpe 2020-07-31 14:21 ` Greg Kroah-Hartman [this message] 2020-07-31 14:21 ` Greg Kroah-Hartman 2020-07-31 14:36 ` Jason Gunthorpe 2020-07-31 14:36 ` Jason Gunthorpe 2020-07-31 17:19 ` Greg Kroah-Hartman 2020-07-31 17:19 ` Greg Kroah-Hartman 2020-07-31 18:27 ` Jason Gunthorpe 2020-07-31 18:27 ` Jason Gunthorpe 2020-08-01 8:00 ` Dan Carpenter 2020-08-01 8:00 ` Dan Carpenter 2020-08-01 14:40 ` Jason Gunthorpe 2020-08-01 14:40 ` Jason Gunthorpe 2020-08-03 9:34 ` Dan Carpenter 2020-08-03 9:34 ` Dan Carpenter 2020-08-01 5:38 ` Leon Romanovsky 2020-08-01 5:38 ` Leon Romanovsky 2020-08-02 22:10 ` Jason Gunthorpe 2020-08-02 22:10 ` Jason Gunthorpe 2020-08-02 22:23 ` Joe Perches 2020-08-02 22:23 ` Joe Perches 2020-08-02 22:28 ` Jason Gunthorpe 2020-08-02 22:28 ` Jason Gunthorpe 2020-08-02 22:45 ` Joe Perches 2020-08-02 22:45 ` Joe Perches 2020-08-03 4:58 ` Leon Romanovsky 2020-08-03 4:58 ` Leon Romanovsky 2020-08-03 23:06 ` Jason Gunthorpe 2020-08-03 23:06 ` Jason Gunthorpe 2020-08-08 22:57 ` Jack Leadford 2020-08-08 22:57 ` Jack Leadford 2020-08-09 7:04 ` Leon Romanovsky 2020-08-09 7:04 ` Leon Romanovsky 2020-08-14 17:07 ` Jason Gunthorpe 2020-08-14 17:07 ` Jason Gunthorpe 2020-07-31 6:31 ` Andy Shevchenko 2020-07-31 9:59 ` Dan Carpenter 2020-07-31 9:59 ` Dan Carpenter 2020-07-31 11:14 ` Håkon Bugge 2020-07-31 11:14 ` Håkon Bugge 2020-07-31 11:59 ` Greg Kroah-Hartman 2020-07-31 11:59 ` Greg Kroah-Hartman 2020-07-31 12:03 ` Håkon Bugge 2020-07-31 12:03 ` Håkon Bugge 2020-07-31 23:54 ` David Miller 2020-07-31 23:54 ` David Miller
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