Re: [PATCH 4.19] ext4: fix race condition between ext4_ioctl_setflags and ext4_fiemap

Greg KH
2022-07-15T14:10:47Z

On Fri, Jul 15, 2022 at 10:39:28AM +0800, Baokun Li wrote:
> This patch and problem analysis is based on v4.19 LTS.
> The d3b6f23f7167("ext4: move ext4_fiemap to use iomap framework") patch
> is incorporated in v5.7-rc1. This patch avoids this problem by switching
> to iomap in ext4_fiemap.
>
> Hulk Robot reported a BUG on stable 4.19.252:
> ==================================================================
> kernel BUG at fs/ext4/extents_status.c:762!
> invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 7 PID: 2845 Comm: syz-executor Not tainted 4.19.252 #46
> RIP: 0010:ext4_es_cache_extent+0x30e/0x370
> [...]
> Call Trace:
> ext4_cache_extents+0x238/0x2f0
> ext4_find_extent+0x785/0xa40
> ext4_fiemap+0x36d/0xe90
> do_vfs_ioctl+0x6af/0x1200
> [...]
> ==================================================================
>
> Above issue may happen as follows:
> -------------------------------------
> cpu1 cpu2
> _____________________|_____________________
> do_vfs_ioctl
> ext4_ioctl
> ext4_ioctl_setflags
> ext4_ind_migrate
> do_vfs_ioctl
> ioctl_fiemap
> ext4_fiemap
> ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)
> ext4_fill_fiemap_extents
> down_write(&EXT4_I(inode)->i_data_sem);
> ext4_ext_check_inode
> ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS)
> memset(ei->i_data, 0, sizeof(ei->i_data))
> up_write(&EXT4_I(inode)->i_data_sem);
> down_read(&EXT4_I(inode)->i_data_sem);
> ext4_find_extent
> ext4_cache_extents
> ext4_es_cache_extent
> BUG_ON(end < lblk)
>
> We can easily reproduce this problem with the syzkaller testcase:
> ```
> 02:37:07 executing program 3:
> r0 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file0\x00', 0x26e1, 0x0)
> ioctl$FS_IOC_FSSETXATTR(r0, 0x40086602, &(0x7f0000000080)={0x17e})
> mkdirat(0xffffffffffffff9c, &(0x7f00000000c0)='./file1\x00', 0x1ff)
> r1 = openat(0xffffffffffffff9c, &(0x7f0000000100)='./file1\x00', 0x0, 0x0)
> ioctl$FS_IOC_FIEMAP(r1, 0xc020660b, &(0x7f0000000180)={0x0, 0x1, 0x0, 0xef3, 0x6, []}) (async, rerun: 32)
> ioctl$FS_IOC_FSSETXATTR(r1, 0x40086602, &(0x7f0000000140)={0x17e}) (rerun: 32)
> ```
>
> To solve this issue, we use __generic_block_fiemap() instead of
> generic_block_fiemap() and add inode_lock_shared to avoid race condition.
>
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---
> fs/ext4/extents.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)

What is the git commit id of this change in Linus's tree?

If it is not in Linus's tree, why not?

confused,

greg k-h