CVE-2024-43859

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

f2fs: fix to truncate preallocated blocks in f2fs_file_open()

chenyuwen reports a f2fs bug as below:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000011 fscrypt_set_bio_crypt_ctx+0x78/0x1e8 f2fs_grab_read_bio+0x78/0x208 f2fs_submit_page_read+0x44/0x154 f2fs_get_read_data_page+0x288/0x5f4 f2fs_get_lock_data_page+0x60/0x190 truncate_partial_data_page+0x108/0x4fc f2fs_do_truncate_blocks+0x344/0x5f0 f2fs_truncate_blocks+0x6c/0x134 f2fs_truncate+0xd8/0x200 f2fs_iget+0x20c/0x5ac do_garbage_collect+0x5d0/0xf6c f2fs_gc+0x22c/0x6a4 f2fs_disable_checkpoint+0xc8/0x310 f2fs_fill_super+0x14bc/0x1764 mount_bdev+0x1b4/0x21c f2fs_mount+0x20/0x30 legacy_get_tree+0x50/0xbc vfs_get_tree+0x5c/0x1b0 do_new_mount+0x298/0x4cc path_mount+0x33c/0x5fc __arm64_sys_mount+0xcc/0x15c invoke_syscall+0x60/0x150 el0_svc_common+0xb8/0xf8 do_el0_svc+0x28/0xa0 el0_svc+0x24/0x84 el0t_64_sync_handler+0x88/0xec

It is because inode.i_crypt_info is not initialized during below path:

• mount
• f2fs_fill_super
• f2fs_disable_checkpoint
• f2fs_gc - f2fs_iget
  • f2fs_truncate

So, lets relocate truncation of preallocated blocks to f2fs_file_open(), after fscrypt_file_open().

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/298b1e4182d657c3e388adcc29477904e9600ed5
• https://git.kernel.org/stable/c/3ba0ae885215b325605ff7ebf6de12ac2adf204d
• https://git.kernel.org/stable/c/5f04969136db674f133781626e0b692c5f2bf2f0
• https://git.kernel.org/stable/c/f44a25a8bfe0c15d33244539696cd9119cf44d18