CVE-2021-47007

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

f2fs: fix panic during f2fs_resize_fs()

f2fs_resize_fs() hangs in below callstack with testcase:

• mkfs 16GB image & mount image
• dd 8GB fileA
• dd 8GB fileB
• sync
• rm fileA
• sync
• resize filesystem to 8GB

kernel BUG at segment.c:2484! Call Trace: allocate_segment_by_default+0x92/0xf0 [f2fs] f2fs_allocate_data_block+0x44b/0x7e0 [f2fs] do_write_page+0x5a/0x110 [f2fs] f2fs_outplace_write_data+0x55/0x100 [f2fs] f2fs_do_write_data_page+0x392/0x850 [f2fs] move_data_page+0x233/0x320 [f2fs] do_garbage_collect+0x14d9/0x1660 [f2fs] free_segment_range+0x1f7/0x310 [f2fs] f2fs_resize_fs+0x118/0x330 [f2fs] __f2fs_ioctl+0x487/0x3680 [f2fs] __x64_sys_ioctl+0x8e/0xd0 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The root cause is we forgot to check that whether we have enough space in resized filesystem to store all valid blocks in before-resizing filesystem, then allocator will run out-of-space during block migration in free_segment_range().

Affected Software

References

• https://git.kernel.org/stable/c/1c20a4896409f5ca1c770e1880c33d0a28a8b10f
• https://git.kernel.org/stable/c/3ab0598e6d860ef49d029943ba80f627c15c15d6
• https://git.kernel.org/stable/c/822054e5026c43b1dd60cf387dd999e95ee2ecc2
• https://git.kernel.org/stable/c/860afd680d9cc1dabd61cda3cd246f60aa1eb705