Linux Kernel up to 6.1.92/6.6.32/6.9.3 multidev f2fs_map_blocks comparison

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.1.92/6.6.32/6.9.3. It has been declared as problematic. The affected element is the function f2fs_map_blocks of the component multidev. The manipulation results in comparison. This vulnerability is reported as CVE-2024-38636. No exploit exists. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic has been found in Linux Kernel up to 6.1.92/6.6.32/6.9.3. Affected is the function f2fs_map_blocks of the component multidev. The manipulation with an unknown input leads to a comparison vulnerability. CWE is classifying the issue as CWE-697. The product compares two entities in a security-relevant context, but the comparison is incorrect, which may lead to resultant weaknesses. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: f2fs: multidev: fix to recognize valid zero block address As reported by Yi Zhang in mailing list [1], kernel warning was catched during zbd/010 test as below: ./check zbd/010 zbd/010 (test gap zone support with F2FS) [failed] runtime ... 3.752s something found in dmesg: [ 4378.146781] run blktests zbd/010 at 2024-02-18 11:31:13 [ 4378.192349] null_blk: module loaded [ 4378.209860] null_blk: disk nullb0 created [ 4378.413285] scsi_debug:sdebug_driver_probe: scsi_debug: trim poll_queues to 0. poll_q/nr_hw = (0/1) [ 4378.422334] scsi host15: scsi_debug: version 0191 [20210520] dev_size_mb=1024, opts=0x0, submit_queues=1, statistics=0 [ 4378.434922] scsi 15:0:0:0: Direct-Access-ZBC Linux scsi_debug 0191 PQ: 0 ANSI: 7 [ 4378.443343] scsi 15:0:0:0: Power-on or device reset occurred [ 4378.449371] sd 15:0:0:0: Attached scsi generic sg5 type 20 [ 4378.449418] sd 15:0:0:0: [sdf] Host-managed zoned block device ... (See '/mnt/tests/gitlab.com/api/v4/projects/19168116/repository/archive.zip/storage/blktests/blk/blktests/results/nodev/zbd/010.dmesg' WARNING: CPU: 22 PID: 44011 at fs/iomap/iter.c:51 CPU: 22 PID: 44011 Comm: fio Not tainted 6.8.0-rc3+ #1 RIP: 0010:iomap_iter+0x32b/0x350 Call Trace: __iomap_dio_rw+0x1df/0x830 f2fs_file_read_iter+0x156/0x3d0 [f2fs] aio_read+0x138/0x210 io_submit_one+0x188/0x8c0 __x64_sys_io_submit+0x8c/0x1a0 do_syscall_64+0x86/0x170 entry_SYSCALL_64_after_hwframe+0x6e/0x76 Shinichiro Kawasaki helps to analyse this issue and proposes a potential fixing patch in [2]. Quoted from reply of Shinichiro Kawasaki: "I confirmed that the trigger commit is dbf8e63f48af as Yi reported. I took a look in the commit, but it looks fine to me. So I thought the cause is not in the commit diff. I found the WARN is printed when the f2fs is set up with multiple devices, and read requests are mapped to the very first block of the second device in the direct read path. In this case, f2fs_map_blocks() and f2fs_map_blocks_cached() modify map->m_pblk as the physical block address from each block device. It becomes zero when it is mapped to the first block of the device. However, f2fs_iomap_begin() assumes that map->m_pblk is the physical block address of the whole f2fs, across the all block devices. It compares map->m_pblk against NULL_ADDR == 0, then go into the unexpected branch and sets the invalid iomap->length. The WARN catches the invalid iomap->length. This WARN is printed even for non-zoned block devices, by following steps. - Create two (non-zoned) null_blk devices memory backed with 128MB size each: nullb0 and nullb1. # mkfs.f2fs /dev/nullb0 -c /dev/nullb1 # mount -t f2fs /dev/nullb0 "${mount_dir}" # dd if=/dev/zero of="${mount_dir}/test.dat" bs=1M count=192 # dd if="${mount_dir}/test.dat" of=/dev/null bs=1M count=192 iflag=direct ..." So, the root cause of this issue is: when multi-devices feature is on, f2fs_map_blocks() may return zero blkaddr in non-primary device, which is a verified valid block address, however, f2fs_iomap_begin() treats it as an invalid block address, and then it triggers the warning in iomap framework code. Finally, as discussed, we decide to use a more simple and direct way that checking (map.m_flags & F2FS_MAP_MAPPED) condition instead of (map.m_pblk != NULL_ADDR) to fix this issue. Thanks a lot for the effort of Yi Zhang and Shinichiro Kawasaki on this issue. [1] https://lore.kernel.org/linux-f2fs-devel/CAHj4cs-kfojYC9i0G73PRkYzcxCTex=-vugRFeP40g_URGvnfQ@mail.gmail.com/ [2] https://lore.kernel.org/linux-f2fs-devel/gngdj77k4picagsfdtiaa7gpgnup6fsgwzsltx6milmhegmjff@iax2n4wvrqye/

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2024-38636 since 06/18/2024. The exploitability is told to be difficult. There are known technical details, but no exploit is available.

Upgrading to version 6.1.93, 6.6.33 or 6.9.4 eliminates this vulnerability. Applying the patch 1a9225fdd0ec/2b2611a42462/e8b485e39b4d/33e62cd7b4c2 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.1.0
• 6.1.1
• 6.1.2
• 6.1.3
• 6.1.4
• 6.1.5
• 6.1.6
• 6.1.7
• 6.1.8
• 6.1.9
• 6.1.10
• 6.1.11
• 6.1.12
• 6.1.13
• 6.1.14
• 6.1.15
• 6.1.16
• 6.1.17
• 6.1.18
• 6.1.19
• 6.1.20
• 6.1.21
• 6.1.22
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• 6.1.24
• 6.1.25
• 6.1.26
• 6.1.27
• 6.1.28
• 6.1.29
• 6.1.30
• 6.1.31
• 6.1.32
• 6.1.33
• 6.1.34
• 6.1.35
• 6.1.36
• 6.1.37
• 6.1.38
• 6.1.39
• 6.1.40
• 6.1.41
• 6.1.42
• 6.1.43
• 6.1.44
• 6.1.45
• 6.1.46
• 6.1.47
• 6.1.48
• 6.1.49
• 6.1.50
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• 6.1.56
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• 6.1.69
• 6.1.70
• 6.1.71
• 6.1.72
• 6.1.73
• 6.1.74
• 6.1.75
• 6.1.76
• 6.1.77
• 6.1.78
• 6.1.79
• 6.1.80
• 6.1.81
• 6.1.82
• 6.1.83
• 6.1.84
• 6.1.85
• 6.1.86
• 6.1.87
• 6.1.88
• 6.1.89
• 6.1.90
• 6.1.91
• 6.1.92
• 6.6.0
• 6.6.1
• 6.6.2
• 6.6.3
• 6.6.4
• 6.6.5
• 6.6.6
• 6.6.7
• 6.6.8
• 6.6.9
• 6.6.10
• 6.6.11
• 6.6.12
• 6.6.13
• 6.6.14
• 6.6.15
• 6.6.16
• 6.6.17
• 6.6.18
• 6.6.19
• 6.6.20
• 6.6.21
• 6.6.22
• 6.6.23
• 6.6.24
• 6.6.25
• 6.6.26
• 6.6.27
• 6.6.28
• 6.6.29
• 6.6.30
• 6.6.31
• 6.6.32
• 6.9.0
• 6.9.1
• 6.9.2
• 6.9.3

License

• open-source

Website

• Vendor: https://www.kernel.org/

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