linux-kernel - Re: [PATCH 3/4] ext4: avoid overlapping preallocations due to overflow

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Message-Id: <87351io074.fsf@doe.com>
Date:   Fri, 21 Jul 2023 00:54:47 +0530
From:   Ritesh Harjani (IBM) <ritesh.list@...il.com>
To:     Baokun Li <libaokun1@...wei.com>, linux-ext4@...r.kernel.org
Cc:     tytso@....edu, adilger.kernel@...ger.ca, jack@...e.cz,
        ojaswin@...ux.ibm.com, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com, yukuai3@...wei.com,
        libaokun1@...wei.com
Subject: Re: [PATCH 3/4] ext4: avoid overlapping preallocations due to overflow

Baokun Li <libaokun1@...wei.com> writes:

> Let's say we want to allocate 2 blocks starting from 4294966386, after
> predicting the file size, start is aligned to 4294965248, len is changed
> to 2048, then end = start + size = 0x100000000. Since end is of
> type ext4_lblk_t, i.e. uint, end is truncated to 0.
>
> This causes (pa->pa_lstart >= end) to always hold when checking if the
> current extent to be allocated crosses already preallocated blocks, so the
> resulting ac_g_ex may cross already preallocated blocks.
>
> Hence we convert the end type to loff_t and use pa_end() to avoid overflow.
>
> Signed-off-by: Baokun Li <libaokun1@...wei.com>

Thanks again for spotting. Looks good to me (with pa_end() dropped).

-ritesh


> ---
>  fs/ext4/mballoc.c | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 2090e5e7ba58..77d47af525d9 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4222,12 +4222,13 @@ ext4_mb_pa_rb_next_iter(ext4_lblk_t new_start, ext4_lblk_t cur_start, struct rb_
>  
>  static inline void
>  ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
> -			  ext4_lblk_t start, ext4_lblk_t end)
> +			  ext4_lblk_t start, loff_t end)
>  {
>  	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
>  	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
>  	struct ext4_prealloc_space *tmp_pa;
> -	ext4_lblk_t tmp_pa_start, tmp_pa_end;
> +	ext4_lblk_t tmp_pa_start;
> +	loff_t tmp_pa_end;
>  	struct rb_node *iter;
>  
>  	read_lock(&ei->i_prealloc_lock);
> @@ -4236,7 +4237,7 @@ ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
>  		tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
>  				  pa_node.inode_node);
>  		tmp_pa_start = tmp_pa->pa_lstart;
> -		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
> +		tmp_pa_end = pa_end(sbi, tmp_pa);
>  
>  		spin_lock(&tmp_pa->pa_lock);
>  		if (tmp_pa->pa_deleted == 0)
> @@ -4258,14 +4259,14 @@ ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
>   */
>  static inline void
>  ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
> -			  ext4_lblk_t *start, ext4_lblk_t *end)
> +			  ext4_lblk_t *start, loff_t *end)
>  {
>  	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
>  	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
>  	struct ext4_prealloc_space *tmp_pa = NULL, *left_pa = NULL, *right_pa = NULL;
>  	struct rb_node *iter;
> -	ext4_lblk_t new_start, new_end;
> -	ext4_lblk_t tmp_pa_start, tmp_pa_end, left_pa_end = -1, right_pa_start = -1;
> +	ext4_lblk_t new_start, tmp_pa_start, right_pa_start = -1;
> +	loff_t new_end, tmp_pa_end, left_pa_end = -1;
>  
>  	new_start = *start;
>  	new_end = *end;
> @@ -4284,7 +4285,7 @@ ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
>  		tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
>  				  pa_node.inode_node);
>  		tmp_pa_start = tmp_pa->pa_lstart;
> -		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
> +		tmp_pa_end = pa_end(sbi, tmp_pa);
>  
>  		/* PA must not overlap original request */
>  		spin_lock(&tmp_pa->pa_lock);
> @@ -4364,8 +4365,7 @@ ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
>  	}
>  
>  	if (left_pa) {
> -		left_pa_end =
> -			left_pa->pa_lstart + EXT4_C2B(sbi, left_pa->pa_len);
> +		left_pa_end = pa_end(sbi, left_pa);
>  		BUG_ON(left_pa_end > ac->ac_o_ex.fe_logical);
>  	}
>  
> @@ -4404,8 +4404,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>  	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
>  	struct ext4_super_block *es = sbi->s_es;
>  	int bsbits, max;
> -	ext4_lblk_t end;
> -	loff_t size, start_off;
> +	loff_t size, start_off, end;
>  	loff_t orig_size __maybe_unused;
>  	ext4_lblk_t start;
>  
> -- 
> 2.31.1