Re: panic while mounting msdosfs

[Jukka Salmi <j+nbsd%2008.salmi.ch@localhost>]

Antti Kantee --> current-users (2008-01-04 02:31:30 +0200):
> On Thu Jan 03 2008 at 23:26:33 +0100, Jukka Salmi wrote:
> > Antti Kantee --> current-users (2008-01-03 18:30:35 +0200):
> > > On Thu Jan 03 2008 at 16:54:07 +0100, Jukka Salmi wrote:
> > > > Hi,
> > > > 
> > > > a NetBSD/i386 4.99.47 system reproducibly panics while mounting a msdos
> > > > file system:
> > > > 
> > > > $ vnconfig vnd0 /tmp/msdosfs
> > > 
> > > Where did the image come from and can you share it?
> > 
> > It was on a CF card I got from a friend; it's probably a corrupted
> > file system. And yes, I can share it. I'll contact you off-list.
> 
> Ok, first how to analyze it in a slightly easier env:
> rump/fs/bin/msdosfs> ./msdosfs ~/img/msdosfs.img /mnt
> buf mem pool index 23
> Abort (core dumped)
> 
> Next, seems like the file system is not FAT enough:
> (gdb) p/x *b710
> $1 = {bpbBytesPerSec = {0x2, 0x0}, bpbSecPerClust = 0x8, bpbResSectors = 
> {0x0, 
>     0x2}, bpbFATs = 0x2, bpbRootDirEnts = {0x0, 0x0}, bpbSectors = {0x0, 
> 0x0}, 
>   bpbMedia = 0xf8, bpbFATsecs = {0x0, 0x0}, bpbSecPerTrack = {0x3f, 0x0}, 
>   bpbHeads = {0xff, 0x0}, bpbHiddenSecs = {0x0, 0x0, 0x0, 0x0}, 
>   bpbHugeSectors = {0xb1, 0xd4, 0x79, 0x0}, bpbBigFATsecs = {0x0, 0x0, 0x0, 
>     0x0}, bpbExtFlags = {0x0, 0x0}, bpbFSVers = {0x0, 0x0}, bpbRootClust = {
>     0x0, 0x0, 0x0, 0x0}, bpbFSInfo = {0x0, 0x0}, bpbBackup = {0x0, 0x0}, 
>   bpbReserved = {0x0 <repeats 12 times>}}
> 
> bpbBigFATsecs is 0.  This means that the file allocation table is 0 bytes
> in size.  Not much info will fit into 0 bytes ...  Anyway, this causes
> the fs to try to read 0 bytes using bread().  bread() does not like
> being bothered with such trivial tasks and panics the kernel as revenge.
> 
> The attached patch (I'll commit it soon) refuses to mount non-fatty FATs:
> rump/fs/bin/msdosfs> ./msdosfs ~/img/msdosfs.img /mnt
> msdosfs: VFS_MOUNT 22
> msdosfs: mount: Invalid argument
> 
> I'm curious though, can you try using the file system image on any
> other OS?

Linux is able to mount it (while printing lots of warnings), sees some
directories and files, but trying to read these files results in I/O
errors.


> Index: msdosfs_vfsops.c
> ===================================================================
> RCS file: /cvsroot/src/sys/fs/msdosfs/msdosfs_vfsops.c,v
> retrieving revision 1.57
> diff -p -u -r1.57 msdosfs_vfsops.c
> --- msdosfs_vfsops.c  3 Jan 2008 01:26:28 -0000       1.57
> +++ msdosfs_vfsops.c  4 Jan 2008 00:31:16 -0000
> @@ -638,6 +638,14 @@ msdosfs_mountfs(devvp, mp, l, argp)
>               pmp->pm_FATsecs     *= tmp;
>               SecPerClust         *= tmp;
>       }
> +
> +     /* Check that fs has nonzero FAT size */
> +     if (pmp->pm_FATsecs == 0) {
> +             DPRINTF(("FATsecs is 0\n"));
> +             error = EINVAL;
> +             goto error_exit;
> +     }
> +
>       pmp->pm_fatblk = pmp->pm_ResSectors;
>       if (FAT32(pmp)) {
>               pmp->pm_rootdirblk = getulong(b710->bpbRootClust);

Thanks!


Regards, Jukka

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