Re: panic while mounting msdosfs

[Antti Kantee <pooka%cs.hut.fi@localhost>]

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?

-- 
Antti Kantee <pooka%iki.fi@localhost>                     Of course he runs 
NetBSD
http://www.iki.fi/pooka/                          http://www.NetBSD.org/
    "la qualité la plus indispensable du cuisinier est l'exactitude"

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);