CVE-2023-52705 Information

Description

In the Linux kernel the following vulnerability has been resolved:

nilfs2: fix underflow in second superblock position calculations

Macro NILFS_SB2_OFFSET_BYTES which computes the position of the second superblock underflows when the argument device size is less than 4096 bytes. Therefore when using this macro it is necessary to check in advance that the device size is not less than a lower limit or at least that underflow does not occur.

The current nilfs2 implementation lacks this check causing out-of-bound block access when mounting devices smaller than 4096 bytes:

I/O error dev loop0 sector 36028797018963960 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 NILFS (loop0): unable to read secondary superblock (blocksize = 1024)

In addition when trying to resize the filesystem to a size below 4096 bytes this underflow occurs in nilfs_resize_fs() passing a huge number of segments to nilfs_sufile_resize() corrupting parameters such as the number of segments in superblocks. This causes excessive loop iterations in nilfs_sufile_resize() during a subsequent resize ioctl causing semaphore ns_segctor_sem to block for a long time and hang the writer thread:

INFO: task segctord:5067 blocked for more than 143 seconds. Not tainted 6.2.0-rc8-syzkaller-00015-gf6feea56f66d 0 cho 0 > /proc/sys/kernel/hung_task_timeout_secs\ disables this message. task:segctord state:D stack:23456 pid:5067 ppid:2 flags:0x00004000 Call Trace: context_switch kernel/sched/core.c:5293 [inline] __schedule+0x1409/0x43f0 kernel/sched/core.c:6606 schedule+0xc3/0x190 kernel/sched/core.c:6682 rwsem_down_write_slowpath+0xfcf/0x14a0 kernel/locking/rwsem.c:1190 nilfs_transaction_lock+0x25c/0x4f0 fs/nilfs2/segment.c:357 nilfs_segctor_thread_construct fs/nilfs2/segment.c:2486 [inline] nilfs_segctor_thread+0x52f/0x1140 fs/nilfs2/segment.c:2570 kthread+0x270/0x300 kernel/kthread.c:376 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 … Call Trace: folio_mark_accessed+0x51c/0xf00 mm/swap.c:515 __nilfs_get_page_block fs/nilfs2/page.c:42 [inline] nilfs_grab_buffer+0x3d3/0x540 fs/nilfs2/page.c:61 nilfs_mdt_submit_block+0xd7/0x8f0 fs/nilfs2/mdt.c:121 nilfs_mdt_read_block+0xeb/0x430 fs/nilfs2/mdt.c:176 nilfs_mdt_get_block+0x12d/0xbb0 fs/nilfs2/mdt.c:251 nilfs_sufile_get_segment_usage_block fs/nilfs2/sufile.c:92 [inline] nilfs_sufile_truncate_range fs/nilfs2/sufile.c:679 [inline] nilfs_sufile_resize+0x7a3/0x12b0 fs/nilfs2/sufile.c:777 nilfs_resize_fs+0x20c/0xed0 fs/nilfs2/super.c:422 nilfs_ioctl_resize fs/nilfs2/ioctl.c:1033 [inline] nilfs_ioctl+0x137c/0x2440 fs/nilfs2/ioctl.c:1301 …

This fixes these issues by inserting appropriate minimum device size checks or anti-underflow checks depending on where the macro is used.

Reference

https://git.kernel.org/stable/c/2f7a1135b202977b82457adde7db6c390056863b https://git.kernel.org/stable/c/b96591e2c35c8b47db0ec816b5fc6cb8868000ff https://git.kernel.org/stable/c/52844d8382cd9166d708032def8905ffc3ae550f https://git.kernel.org/stable/c/0ee5ed0126a2211f7174492da2ca2c29f43755c5 https://git.kernel.org/stable/c/a158782b56b070485d54d25fc9aaf2c8f3752205 https://git.kernel.org/stable/c/a8ef5109f93cea9933bbac0455d8c18757b3fcb4 https://git.kernel.org/stable/c/99b9402a36f0799f25feee4465bfa4b8dfa74b4d