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Message-ID: <688c8528-f681-cd6e-d16d-5ecc2e21a75d@huawei.com>
Date: Fri, 21 Jul 2023 16:01:52 +0800
From: Baokun Li <libaokun1@...wei.com>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.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>, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH 2/4] ext4: fix BUG in ext4_mb_new_inode_pa() due to
overflow
On 2023/7/21 3:07, Ritesh Harjani (IBM) wrote:
> Baokun Li <libaokun1@...wei.com> writes:
>
>> When we calculate the end position of ext4_free_extent, this position may
>> be exactly where ext4_lblk_t (i.e. uint) overflows. For example, if
>> ac_g_ex.fe_logical is 4294965248 and ac_orig_goal_len is 2048, then the
>> computed end is 0x100000000, which is 0. If ac->ac_o_ex.fe_logical is not
>> the first case of adjusting the best extent, that is, new_bex_end > 0, the
>> following BUG_ON will be triggered:
>>
>> =========================================================
>> kernel BUG at fs/ext4/mballoc.c:5116!
>> invalid opcode: 0000 [#1] PREEMPT SMP PTI
>> CPU: 3 PID: 673 Comm: xfs_io Tainted: G E 6.5.0-rc1+ #279
>> RIP: 0010:ext4_mb_new_inode_pa+0xc5/0x430
>> Call Trace:
>> <TASK>
>> ext4_mb_use_best_found+0x203/0x2f0
>> ext4_mb_try_best_found+0x163/0x240
>> ext4_mb_regular_allocator+0x158/0x1550
>> ext4_mb_new_blocks+0x86a/0xe10
>> ext4_ext_map_blocks+0xb0c/0x13a0
>> ext4_map_blocks+0x2cd/0x8f0
>> ext4_iomap_begin+0x27b/0x400
>> iomap_iter+0x222/0x3d0
>> __iomap_dio_rw+0x243/0xcb0
>> iomap_dio_rw+0x16/0x80
>> =========================================================
>>
>> A simple reproducer demonstrating the problem:
>>
>> mkfs.ext4 -F /dev/sda -b 4096 100M
>> mount /dev/sda /tmp/test
>> fallocate -l1M /tmp/test/tmp
>> fallocate -l10M /tmp/test/file
>> fallocate -i -o 1M -l16777203M /tmp/test/file
>> fsstress -d /tmp/test -l 0 -n 100000 -p 8 &
>> sleep 10 && killall -9 fsstress
>> rm -f /tmp/test/tmp
>> xfs_io -c "open -ad /tmp/test/file" -c "pwrite -S 0xff 0 8192"
>>
>> We declare new_bex_start and new_bex_end as correct types and use fex_end()
>> to avoid the problems caused by the ext4_lblk_t overflow above.
>>
>> Fixes: 93cdf49f6eca ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()")
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
>> ---
>> fs/ext4/mballoc.c | 11 +++++------
>> 1 file changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index eb7f5d35ef96..2090e5e7ba58 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -5076,8 +5076,8 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
>> pa = ac->ac_pa;
>>
>> if (ac->ac_b_ex.fe_len < ac->ac_orig_goal_len) {
>> - int new_bex_start;
>> - int new_bex_end;
>> + ext4_lblk_t new_bex_start;
>> + loff_t new_bex_end;
>>
>> /* we can't allocate as much as normalizer wants.
>> * so, found space must get proper lstart
>> @@ -5096,8 +5096,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
>> * still cover original start
>> * 3. Else, keep the best ex at start of original request.
>> */
>> - new_bex_end = ac->ac_g_ex.fe_logical +
>> - EXT4_C2B(sbi, ac->ac_orig_goal_len);
>> + new_bex_end = fex_end(sbi, &ac->ac_g_ex, &ac->ac_orig_goal_len);
>> new_bex_start = new_bex_end - EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
>> if (ac->ac_o_ex.fe_logical >= new_bex_start)
>> goto adjust_bex;
> new_bex_end = ac->ac_g_ex.fe_logical +
> EXT4_C2B(sbi, ac->ac_orig_goal_len);
> new_bex_start = new_bex_end - EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
> if (ac->ac_o_ex.fe_logical >= new_bex_start)
> goto adjust_bex;
>
> new_bex_start = ac->ac_g_ex.fe_logical;
> new_bex_end =
> new_bex_start + EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
> if (ac->ac_o_ex.fe_logical < new_bex_end)
> goto adjust_bex;
>
> new_bex_start = ac->ac_o_ex.fe_logical;
> new_bex_end =
> new_bex_start + EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
>
> I think it will be safer if we typecast all above new_bex_end
> calculations. I understand that it might never happen here that
> fe_logical + best found extent length will make it overflow.
> Simply because we only enter here when ac_b_ex.fe_len <
> ac_orig_goal_len. But I think if we change any logic tomorrow or
> refactor any part of code, it will be much safer if we simply keep the
> typecast in place so that we avoid any future tripping caused by
> arithmatic overflow here.
>
> Also I am not finding fex_end() or pa_end() helpers very intuitive way
> of doing it. I feel typecasting in place is much simpler and reads better.
>
> -ritesh
I remove the third parameter of fex_end() and adjust the code in
ext4_mb_new_inode_pa() as follows:
struct ext4_free_extent ex = {
.fe_logical = ac->ac_g_ex.fe_logical,
.fe_len = ac->ac_orig_goal_len,
};
loff_t orig_goal_end = fex_end(sbi, &ex);
ex.fe_len = ac->ac_b_ex.fe_len;
ex.fe_logical = orig_goal_end - EXT4_C2B(sbi, ex.fe_len);
if (ac->ac_o_ex.fe_logical >= ex.fe_logical)
goto adjust_bex;
ex.fe_logical = ac->ac_g_ex.fe_logical;
if (ac->ac_o_ex.fe_logical < fex_end(sbi, &ex))
goto adjust_bex;
ex.fe_logical = ac->ac_o_ex.fe_logical;
adjust_bex:
ac->ac_b_ex.fe_logical = ex.fe_logical;
BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
BUG_ON(fex_end(sbi, &ex) > orig_goal_end);
In this way, all new_bex_end calculations do not have overflow problems,
and the code looks much more neat than before. 😊
>> @@ -5117,8 +5116,8 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
>>
>> BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
>> BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
>> - BUG_ON(new_bex_end > (ac->ac_g_ex.fe_logical +
>> - EXT4_C2B(sbi, ac->ac_orig_goal_len)));
>> + BUG_ON(new_bex_end >
>> + fex_end(sbi, &ac->ac_g_ex, &ac->ac_orig_goal_len));
>> }
>>
>> pa->pa_lstart = ac->ac_b_ex.fe_logical;
>> --
>> 2.31.1
Thanks!
--
With Best Regards,
Baokun Li
.
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