On Tue, 6 Sep 2011, Tao Ma wrote:
> Hi Lucas,
> On 09/05/2011 10:34 PM, Lukas Czerner wrote:
> > In ext4_trim_fs it is possible that start+len might overflow. Fix it by
> > decrementing the len so that start+len equals to the file system size in
> > the worst case.
> Actually start + len can never overflow since they are changed by
> start = range->start >> sb->s_blocksize_bits;
> len = range->len >> sb->s_blocksize_bits;
>
> range->start and range->len are u64, and after they are shifted with
> blocksize_bits, start+len(ext4_fsblk_t is also 64bit) can't overflow.
>
> Thanks
> Tao
Hi Tao,
I am really sorry for badly worded commit description. The problem is
real, however as you pointed out the overflow does not happen in
len+start addition but in ext4_get_group_no_and_offset() when we are
storing group number into the ext4_group_t which is 32 bit long, but
the result of do_div() might be bigger than that.
I will rephrase the commit description and resend the patch. I was doing
similar thing for xfs and I have just used almost the same description
which is wrong.
Thanks!
-Lukas
> >
> > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> > ---
> > fs/ext4/mballoc.c | 6 +++++-
> > 1 files changed, 5 insertions(+), 1 deletions(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 17a5a57..d86dc14 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -4952,14 +4952,18 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> > uint64_t start, len, minlen, trimmed = 0;
> > ext4_fsblk_t first_data_blk =
> > le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
> > + ext4_fsblk_t max_blks = ext4_blocks_count(EXT4_SB(sb)->s_es);
> > int ret = 0;
> >
> > start = range->start >> sb->s_blocksize_bits;
> > len = range->len >> sb->s_blocksize_bits;
> > minlen = range->minlen >> sb->s_blocksize_bits;
> >
> > - if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
> > + if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)) ||
> > + unlikely(start > max_blks))
> > return -EINVAL;
> > + if (unlikely(len > max_blks))
> > + len = max_blks - start;
> > if (start + len <= first_data_blk)
> > goto out;
> > if (start < first_data_blk) {
>
>
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