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Date: Fri, 2 Mar 2012 11:52:10 +0100 (CET)
From: Lukas Czerner <lczerner@...hat.com>
To: Jan Kara <jack@...e.cz>
cc: Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org,
tytso@....edu
Subject: Re: [PATCH 1/2] ext3: fix start and len arguments handling in
ext3_trim_fs()
On Fri, 2 Mar 2012, Jan Kara wrote:
> On Thu 01-03-12 14:40:06, Lukas Czerner wrote:
> > The overflow might happen when passing blocknr into
> > ext3_get_group_no_and_offset(), because it expects type ext3_fsblk_t
> > which might be smaller than uint64_t. This will most likely happen when
> > calling FITRIM with the default argument len = ULLONG_MAX.
> >
> > Fix this by using "end" variable instead of "start+len" as it is easier
> > to get right and specifically check that the end is not beyond the end
> > of the file system, so we are sure that the result of
> > get_group_no_and_offset() will not overflow. Otherwise truncate it to
> > the size of the file system.
> >
> > Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> Please CC me on ext3 patches. Thanks.
Sure, I forgot about that.
>
> > ---
> > fs/ext3/balloc.c | 73 +++++++++++++++++++++++++++--------------------------
> > 1 files changed, 37 insertions(+), 36 deletions(-)
> >
> > diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
> > index a203892..e3a8d9e 100644
> > --- a/fs/ext3/balloc.c
> > +++ b/fs/ext3/balloc.c
> > @@ -2091,73 +2091,74 @@ err_out:
> > */
> > int ext3_trim_fs(struct super_block *sb, struct fstrim_range *range)
> > {
> > - ext3_grpblk_t last_block, first_block, free_blocks;
> > - unsigned long first_group, last_group;
> > - unsigned long group, ngroups;
> > + ext3_grpblk_t last_block, first_block;
> > + unsigned long group, first_group, last_group;
> > struct ext3_group_desc *gdp;
> > struct ext3_super_block *es = EXT3_SB(sb)->s_es;
> > - uint64_t start, len, minlen, trimmed;
> > + uint64_t start, minlen, end, trimmed = 0;
> > + ext3_fsblk_t first_data_blk =
> > + le32_to_cpu(EXT3_SB(sb)->s_es->s_first_data_block);
> > ext3_fsblk_t max_blks = le32_to_cpu(es->s_blocks_count);
> > int ret = 0;
> >
> > - start = (range->start >> sb->s_blocksize_bits) +
> > - le32_to_cpu(es->s_first_data_block);
> > - len = range->len >> sb->s_blocksize_bits;
> > + start = range->start >> sb->s_blocksize_bits;
> > + end = start + (range->len >> sb->s_blocksize_bits) - 1;
> > minlen = range->minlen >> sb->s_blocksize_bits;
> > - trimmed = 0;
> >
> > - if (unlikely(minlen > EXT3_BLOCKS_PER_GROUP(sb)))
> > + if (unlikely(minlen > EXT3_BLOCKS_PER_GROUP(sb)) ||
> > + unlikely(start >= max_blks))
> > return -EINVAL;
> > - if (start >= max_blks)
> > - return -EINVAL;
> > - if (start + len > max_blks)
> > - len = max_blks - start;
> > + if (end >= max_blks)
> > + end = max_blks - 1;
> > + if (end <= first_data_blk)
> > + goto out;
> > + if (start < first_data_blk)
> > + start = first_data_blk;
> Hmm, but this changed slighthly how trimming behaves with
> s_first_data_block > 0. Originally, if I submitted trim with start == 0,
> len == 1024, it would trim a single 1k block. Now it won't trim anything?
> I see ext4 does it this way as well and probably noone would notice but I
> want to have this clear...
Yes, it is changed. I wanted the ext4 and ext3 implementation to be as
close as possible.
Thanks for review.
-Lukas
>
> > - ngroups = EXT3_SB(sb)->s_groups_count;
> > smp_rmb();
> >
> > /* Determine first and last group to examine based on start and len */
> > ext3_get_group_no_and_offset(sb, (ext3_fsblk_t) start,
> > &first_group, &first_block);
> > - ext3_get_group_no_and_offset(sb, (ext3_fsblk_t) (start + len),
> > + ext3_get_group_no_and_offset(sb, (ext3_fsblk_t) end,
> > &last_group, &last_block);
> > - last_group = (last_group > ngroups - 1) ? ngroups - 1 : last_group;
> > - last_block = EXT3_BLOCKS_PER_GROUP(sb);
> >
> > - if (first_group > last_group)
> > - return -EINVAL;
> > + /* end now represents the last block to discard in this group */
> > + end = EXT3_BLOCKS_PER_GROUP(sb) - 1;
> >
> > for (group = first_group; group <= last_group; group++) {
> > gdp = ext3_get_group_desc(sb, group, NULL);
> > if (!gdp)
> > break;
> >
> > - free_blocks = le16_to_cpu(gdp->bg_free_blocks_count);
> > - if (free_blocks < minlen)
> > - continue;
> > -
> > /*
> > * For all the groups except the last one, last block will
> > - * always be EXT3_BLOCKS_PER_GROUP(sb), so we only need to
> > - * change it for the last group in which case first_block +
> > - * len < EXT3_BLOCKS_PER_GROUP(sb).
> > + * always be EXT3_BLOCKS_PER_GROUP(sb)-1, so we only need to
> > + * change it for the last group, note that last_block is
> > + * already computed earlier by ext3_get_group_no_and_offset()
> > */
> > - if (first_block + len < EXT3_BLOCKS_PER_GROUP(sb))
> > - last_block = first_block + len;
> > - len -= last_block - first_block;
> > + if (group == last_group)
> > + end = last_block;
> >
> > - ret = ext3_trim_all_free(sb, group, first_block,
> > - last_block, minlen);
> > - if (ret < 0)
> > - break;
> > + if (le16_to_cpu(gdp->bg_free_blocks_count) >= minlen) {
> > + ret = ext3_trim_all_free(sb, group, first_block,
> > + end, minlen);
> > + if (ret < 0)
> > + break;
> > + trimmed += ret;
> > + }
> >
> > - trimmed += ret;
> > + /*
> > + * For every group except the first one, we are sure
> > + * that the first block to discard will be block #0.
> > + */
> > first_block = 0;
> > }
> >
> > - if (ret >= 0)
> > + if (ret > 0)
> > ret = 0;
> > - range->len = trimmed * sb->s_blocksize;
> >
> > +out:
> > + range->len = trimmed * sb->s_blocksize;
> > return ret;
> > }
> > --
> Otherwise the patch looks OK.
>
> Honza
>
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