Messages in this thread | | | Date | Thu, 4 Sep 2008 22:38:36 -0700 | From | Andrew Morton <> | Subject | Re: __getblk infinite loop |
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On Thu, 4 Sep 2008 23:24:11 -0400 Bob Copeland <me@bobcopeland.com> wrote:
> Hi all, > > Eric Sesterhenn and I were puzzling over a lockup found by his fsfuzzer. > > sb_bread() calls __getblk, which says: > > /* > * __getblk will locate (and, if necessary, create) the buffer_head > * which corresponds to the passed block_device, block and size. The > * returned buffer has its reference count incremented. > * > * __getblk() cannot fail - it just keeps trying. If you pass it an > * illegal block number, __getblk() will happily return a buffer_head > * which represents the non-existent block. Very weird. > * > * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers() > * attempt is failing. FIXME, perhaps? > */ > > In fact the following will cause an infinite loop when mounting omfs > loopback (on 32 bit x86 at least): > > diff --git a/fs/omfs/inode.c b/fs/omfs/inode.c > index a95fe59..80eacc8 100644 > --- a/fs/omfs/inode.c > +++ b/fs/omfs/inode.c > @@ -413,6 +413,15 @@ static int omfs_fill_super(struct super_block *sb, void *data, int silent) > sector_t start; > int ret = -EINVAL; > > + if (1) { > + sector_t foo = 0x1d4000004ULL; > + > + sb_set_blocksize(sb, 2048); > + bh = sb_bread(sb, foo); > + brelse(bh); > + goto end; > + } > + > save_mount_options(sb, (char *) data); > > sbi = kzalloc(sizeof(struct omfs_sb_info), GFP_KERNEL); > > What's supposed to happen here? I would have thought that sb_bread > would realize foo was outside the block dev and bail out, but instead > it just gets stuck. Do I need to bounds-check anything passed to > sb_bread?
That loop does lock up on people occasionally - last time was in isofs, because it had done an insane set_blocksize() earlier on.
Yes, it's always a case of garbage in, garbage out (or nothing out, as the case may be).
No, it's not particularly programmer-friendly behaviour.
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