linux-ext4 - Re: [PATCH] ext4: limit the number of blocks in one ADD

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Date:   Mon, 30 Aug 2021 15:52:11 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     <tytso@....edu>, <adilger.kernel@...ger.ca>,
        <harshadshirwadkar@...il.com>
CC:     <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: limit the number of blocks in one ADD_RANGE TLV

ping ?

On 8/20/2021 12:45 PM, Hou Tao wrote:
> Now EXT4_FC_TAG_ADD_RANGE uses ext4_extent to track the
> newly-added blocks, but the limit on the max value of
> ee_len field is ignored, and it can lead to BUG_ON as
> shown below when running command "fallocate -l 128M file"
> on a fast_commit-enabled fs:
>
>   kernel BUG at fs/ext4/ext4_extents.h:199!
>   invalid opcode: 0000 [#1] SMP PTI
>   CPU: 3 PID: 624 Comm: fallocate Not tainted 5.14.0-rc6+ #1
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
>   RIP: 0010:ext4_fc_write_inode_data+0x1f3/0x200
>   Call Trace:
>    ? ext4_fc_write_inode+0xf2/0x150
>    ext4_fc_commit+0x93b/0xa00
>    ? ext4_fallocate+0x1ad/0x10d0
>    ext4_sync_file+0x157/0x340
>    ? ext4_sync_file+0x157/0x340
>    vfs_fsync_range+0x49/0x80
>    do_fsync+0x3d/0x70
>    __x64_sys_fsync+0x14/0x20
>    do_syscall_64+0x3b/0xc0
>    entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Simply fixing it by limiting the number of blocks
> in one EXT4_FC_TAG_ADD_RANGE TLV.
>
> Fixes: aa75f4d3daae ("ext4: main fast-commit commit path")
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>  fs/ext4/fast_commit.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> index e8195229c252..782d05a3f97a 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> @@ -893,6 +893,12 @@ static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc)
>  					    sizeof(lrange), (u8 *)&lrange, crc))
>  				return -ENOSPC;
>  		} else {
> +			unsigned int max = (map.m_flags & EXT4_MAP_UNWRITTEN) ?
> +				EXT_UNWRITTEN_MAX_LEN : EXT_INIT_MAX_LEN;
> +
> +			/* Limit the number of blocks in one extent */
> +			map.m_len = min(max, map.m_len);
> +
>  			fc_ext.fc_ino = cpu_to_le32(inode->i_ino);
>  			ex = (struct ext4_extent *)&fc_ext.fc_ex;
>  			ex->ee_block = cpu_to_le32(map.m_lblk);