Hi, We found a potential concurrency bug in linux kernel 5.3.11. We were able to reproduce this bug in x86 under specific thread interleavings. This bug causes a “bad header/extent” EXT4-fs error. In addition, we think this bug may be related to another bug we reported earlier. Similar to a concern mentioned in your reply, this time the inode had a correct checksum but a wrong header data. https://lore.kernel.org/linux-ext4/459EE6E3-1CB2-4898-8C5F-283E821B2A75@xxxxxxxxx/T/#t ------------------------------------------ Kernel console output EXT4-fs error (device sda1): ext4_ext_check_inode:498: inode #5: comm ski-executor: pblk 0 bad header/extent: invalid magic - magic 0, entries 0, max 0(0), depth 0(0) ------------------------------------------ Test input This bug occurs when a kernel test program is executed twice in different threads and ran concurrently. Our analysis has located that it happens when syscall ioctl with the EXT4_IOC_SWAP_BOOT flag is called twice and interleaves with itself. The test program is generated by Syzkaller as follows: r0 = creat(&(0x7f0000000080)='./file0\x00', 0x0) ioctl$FS_IOC_SETFLAGS(r0, 0x40046602, &(0x7f0000000040)) r1 = creat(&(0x7f0000000000)='./file0\x00', 0x0) pwrite64(r1, &(0x7f00000000c0)='\x00', 0x1, 0x1010000) r2 = creat(&(0x7f0000000000)='./file0\x00', 0x0) ioctl$EXT4_IOC_SWAP_BOOT(r2, 0x6611) ------------------------------------------ Thread interleaving Our analysis revealed that the following interleaving triggers this bug. CPU0 CPU1 swap_inode_boot_loader() … -- ext4_mark_inode_dirty() [fs/ext4/ioctl.c:207] [context switch] swap_inode_boot_loader() -- ext4_iget() ---- ext4_isize() [context switch] … -- ext4_mark_inode_dirty() [fs/ext4/ioctl.c:223] ---- ext4_mark_iloc_dirty() ------ ext4_do_update_inode() for (block = 0; block < EXT4_N_BLOCKS; block++) [fs/ext4/inode.c:5337] raw_inode->i_block[block] = ei->i_data[block]; … [syscall finishes] [context switch] … for (block = 0; block < EXT4_N_BLOCKS; block++) [fs/ext4/inode.c:5002] ei->i_data[block] = raw_inode->i_block[block]; … ---- ext4_ext_check_inode(inode) [EXT4-fs error] Thanks, Sishuai
