ext4: zero i_disksize when initializing the bootloader inode

Overview

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

ext4: zero i_disksize when initializing the bootloader inode

If the boot loader inode has never been used before, the EXT4_IOC_SWAP_BOOT inode will initialize it, including setting the i_size to 0. However, if the "never before used" boot loader has a non-zero i_size, then i_disksize will be non-zero, and the inconsistency between i_size and i_disksize can trigger a kernel warning:

WARNING: CPU: 0 PID: 2580 at fs/ext4/file.c:319 CPU: 0 PID: 2580 Comm: bb Not tainted 6.3.0-rc1-00004-g703695902cfa RIP: 0010:ext4_file_write_iter+0xbc7/0xd10 Call Trace: vfs_write+0x3b1/0x5c0 ksys_write+0x77/0x160 __x64_sys_write+0x22/0x30 do_syscall_64+0x39/0x80

Reproducer:

1. create corrupted image and mount it: mke2fs -t ext4 /tmp/foo.img 200 debugfs -wR "sif <5> size 25700" /tmp/foo.img mount -t ext4 /tmp/foo.img /mnt cd /mnt echo 123 > file
2. Run the reproducer program: posix_memalign(&buf, 1024, 1024) fd = open("file", O_RDWR | O_DIRECT); ioctl(fd, EXT4_IOC_SWAP_BOOT); write(fd, buf, 1024);

Fix this by setting i_disksize as well as i_size to zero when initiaizing the boot loader inode.

Affected

• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < d6c1447e483c05dbcfb3ff77ac04237a82070b8c
• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < 59eee0cdf8c036f554add97a4da7c06d7a9ff34a
• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < 0d8a6c9a6415999fee1259ccf1796480c026b7d6
• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < 3f00c476da8fe7c4c34ea16abb55d74127120413
• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < 01a821aacc64d4b05dafd239dbc9b7856686002f
• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < 9cb27b1e76f0cc886ac09055bc41c0ab3f205167
• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < 9e9a4cc5486356158554f6ad73027d8635a48b34
• Linux >= 393d1d1d76933886d5e1ce603214c9987589c6d5 < f5361da1e60d54ec81346aee8e3d8baf1be0b762
• Linux 3.10

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.