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(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index f1bbce4350c4..50f956bda34c 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -5175,16 +5175,21 @@ static int _ext4_fiemap(struct inode *inode, fieinfo->fi_flags &= ~FIEMAP_FLAG_CACHE; }
+ inode_lock_shared(inode); /* fallback to generic here if not in extents fmt */ if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) && - fill == ext4_fill_fiemap_extents) - return generic_block_fiemap(inode, fieinfo, start, len, + fill == ext4_fill_fiemap_extents) { + error = __generic_block_fiemap(inode, fieinfo, start, len, ext4_get_block); + goto out_unlock; + }
if (fill == ext4_fill_es_cache_info) ext4_fiemap_flags &= FIEMAP_FLAG_XATTR; - if (fiemap_check_flags(fieinfo, ext4_fiemap_flags)) - return -EBADR; + if (fiemap_check_flags(fieinfo, ext4_fiemap_flags)) { + error = -EBADR; + goto out_unlock; + }
if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) { error = ext4_xattr_fiemap(inode, fieinfo); @@ -5204,6 +5209,8 @@ static int _ext4_fiemap(struct inode *inode, */ error = fill(inode, start_blk, len_blks, fieinfo); } +out_unlock: + inode_unlock_shared(inode); return error; }