Date: Thu, 28 Nov 2024 15:48:48 +0000 From: rb@gid.co.uk To: Rick Macklem <rick.macklem@gmail.com> Cc: FreeBSD CURRENT <freebsd-current@FreeBSD.org>, Michael Proto <mike@jellydonut.org> Subject: Re: RFC: fixing PR#282995 Message-ID: <4FEA762C-5E0F-4D3F-82D9-DF93CF1BC1F5@gid.co.uk> In-Reply-To: <CAM5tNy6t_nb4pPTr1N=0%2B7jh6PHDuRz2V%2BJm575TCFpZhjje0A@mail.gmail.com> References: <CAM5tNy4YHAPUgZddok1U3Oz3vFB26-FC5M6Ocwx7bZhWm%2BUX4Q@mail.gmail.com> <F949CCDA-D424-4F83-9A0A-EE8ED7C54A10@gid.co.uk> <CAM5tNy6t_nb4pPTr1N=0%2B7jh6PHDuRz2V%2BJm575TCFpZhjje0A@mail.gmail.com>
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> On 28 Nov 2024, at 15:04, Rick Macklem <rick.macklem@gmail.com> wrote: > > On Thu, Nov 28, 2024 at 4:36 AM Bob Bishop <rb@gid.co.uk> wrote: >> >> Hi, >> >>> On 27 Nov 2024, at 21:56, Rick Macklem <rick.macklem@gmail.com> wrote: >>> >>> Hi, >>> >>> PR#282995 reports that the "-alldirs" export option is broken, >>> since it allows an export where the directory path is not a mount point. >>> >>> I'll admit I did not recall this semantic for -alldirs and I now see it is only >>> documented in the "Examples" section of exports(5). >>> >>> Looking at the code, it appears this was broken between releng1 and >>> releng2.0 (about 30years ago) when the call to mount(2) in mountd.c >>> was changed from using the path in the exports line to using f_mntonname. >>> (The check for "it is a mount point" depended on mount(2) failing because >>> the path was not a mount point.) >>> >>> I do believe the semantic is a useful one, >> >> Why? > Suppose /cdrom is where a CD is mounted sometimes. > If this is exported when the CD is not mounted, it will export > the "/" file system. > --> This export is probably not what the sysadmin wanted. > mountd does now generate a warning about this, which > was how the exporter spotted the bug. > For example (the line in /etc/exports): > /cdrom -alldirs > will export "/" to "the world" if /cdrom is not mounted. I will agree that is undesirable. > The example in the exports(5) man page claims the export > line will fail, so "/" would not be exported. This seems like > a better semantic to me. It’s certainly safer but will cause client mounts to fail as well. It would be nicer to export an empty directory. > rick > >> >>> although making it that way >>> after 30years might be construed as a POLA violation? >>> >>> So, what do others think I should do with this? >>> (A) - Patch mountd to enforce the "must be a mount point when -alldirs >>> is specified, plus update exports(5) to state this semantic clearly. >>> or >>> (B) - Patch mountd so that it enforces "must be a mount point when -alldirs >>> is specified, but only enabled via a new mountd command line option. >>> --> ie. Leave the default as not enforced, but allow enforcement based >>> on a new mountd option. >>> - Document this in both exports(5) and mountd(8). >>> or >>> ??? >> >> (C) - Patch mountd so that it enforces "must be a mount point when -alldirs >> is specified, but provide a new mountd command line option to restore the old behaviour. >> --> ie. Default as enforced, but allow an override based on a new mountd option. >> - Document this in both exports(5) and mountd(8). >> >> I think that (A) is too POLA-unfriendly. >> >>> Thanks in advance for your comments, rick >>> >> >> -- >> Bob Bishop >> rb@gid.co.uk >> >> >> >> > -- Bob Bishop rb@gid.co.ukhome | help
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