Date: Mon, 14 Aug 2017 15:50:58 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> Cc: freebsd-bugs@freebsd.org Subject: Re: [Bug 221501] [msdosfs] panic 11.0-RELEASE by mounting a malformed msdosfs image Message-ID: <20170814153522.C1020@besplex.bde.org> In-Reply-To: <bug-221501-8@https.bugs.freebsd.org/bugzilla/> References: <bug-221501-8@https.bugs.freebsd.org/bugzilla/>
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On Mon, 14 Aug 2017 a big that doesn't want replies@freebsd.org wrote: > It is possible to panic 11.0-RELEASE by mounting a malformed msdosfs image. Did you check it with fsck before mounting? Otherwise the problem is probably uninteresting. No file system in FreeBSD except possibly zfs does much sanity checking at mount time, so it is trivial to construct images that crash it. msdosfs actually does much more sanity checking than ffs. It checks about 100 bytes where ffs checks about 20. However, msdosfs is missing a check of its dirty flag. This doesn't affect crashing it much, but it affects damaging the file system further. ffs allows read-only mounts of dirty images. msdosfs also allows red-write mounts of dirty images. If you run fsck before mounting, then should set the dirty flag if it fails. For ffs, this prevents the read-write case from getting very far. Bruce
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