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

[Greg KH]

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@xxxxxxxxxx>
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> ---
>  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