In the Linux kernel, the following vulnerability has been resolved:

ext4: fix race condition between ext4_write and ext4_convert_inline_data

Hulk Robot reported a BUG_ON:

EXT4-fs error (device loop3): ext4_mb_generate_buddy:805: group 0, block bitmap and bg descriptor inconsistent: 25 vs 31513 free clusters kernel BUG at fs/ext4/ext4_jbd2.c:53! invalid opcode: 0000 [#1] SMP KASAN PTI CPU: 0 PID: 25371 Comm: syz-executor.3 Not tainted 5.10.0+ #1 RIP: 0010:ext4_put_nojournal fs/ext4/ext4_jbd2.c:53 [inline] RIP: 0010:__ext4_journal_stop+0x10e/0x110 fs/ext4/ext4_jbd2.c:116 […] Call Trace: ext4_write_inline_data_end+0x59a/0x730 fs/ext4/inline.c:795 generic_perform_write+0x279/0x3c0 mm/filemap.c:3344 ext4_buffered_write_iter+0x2e3/0x3d0 fs/ext4/file.c:270 ext4_file_write_iter+0x30a/0x11c0 fs/ext4/file.c:520 do_iter_readv_writev+0x339/0x3c0 fs/read_write.c:732 do_iter_write+0x107/0x430 fs/read_write.c:861 vfs_writev fs/read_write.c:934 [inline] do_pwritev+0x1e5/0x380 fs/read_write.c:1031 […]

Above issue may happen as follows: cpu1 cpu2 | do_pwritev vfs_writev do_iter_write ext4_file_write_iter ext4_buffered_write_iter generic_perform_write ext4_da_write_begin vfs_fallocate ext4_fallocate ext4_convert_inline_data ext4_convert_inline_data_nolock ext4_destroy_inline_data_nolock clear EXT4_STATE_MAY_INLINE_DATA ext4_map_blocks ext4_ext_map_blocks ext4_mb_new_blocks ext4_mb_regular_allocator ext4_mb_good_group_nolock ext4_mb_init_group ext4_mb_init_cache ext4_mb_generate_buddy –> error ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) ext4_restore_inline_data set EXT4_STATE_MAY_INLINE_DATA ext4_block_write_begin ext4_da_write_end ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) ext4_write_inline_data_end handle=NULL ext4_journal_stop(handle) __ext4_journal_stop ext4_put_nojournal(handle) ref_cnt = (unsigned long)handle BUG_ON(ref_cnt == 0) —> BUG_ON

The lock held by ext4_convert_inline_data is xattr_sem, but the lock held by generic_perform_write is i_rwsem. Therefore, the two locks can be concurrent.

To solve above issue, we add inode_lock() for ext4_convert_inline_data(). At the same time, move ext4_convert_inline_data() in front of ext4_punch_hole(), remove similar handling from ext4_punch_hole().

Affected Software

References

• https://git.kernel.org/stable/c/14602353b350950b551eccc6b46411aa3b12ffe2
• https://git.kernel.org/stable/c/18881d7e517169193d9ef6c89c7f322e3e164277
• https://git.kernel.org/stable/c/725e00cb7039eae291890f1bb19bc867176745f6
• https://git.kernel.org/stable/c/91f90b571f1a23f5b8a9c2b68a9aa5d6981a3c3d
• https://git.kernel.org/stable/c/ccc6639f831bee91aa8b41c8a1cdd020ecfb9f32
• https://git.kernel.org/stable/c/f87c7a4b084afc13190cbb263538e444cb2b392a