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Date: Fri, 21 Jun 2024 12:20:02 +0200
From: Greg Kroah-Hartman <>
Cc: Greg Kroah-Hartman <>
Subject: CVE-2024-38636: f2fs: multidev: fix to recognize valid zero block address


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/'

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:
 f2fs_file_read_iter+0x156/0x3d0 [f2fs]

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


The Linux kernel CVE team has assigned CVE-2024-38636 to this issue.

Affected and fixed versions

	Issue introduced in 5.17 with commit 1517c1a7a445 and fixed in 6.1.93 with commit 1a9225fdd0ec
	Issue introduced in 5.17 with commit 1517c1a7a445 and fixed in 6.6.33 with commit 2b2611a42462
	Issue introduced in 5.17 with commit 1517c1a7a445 and fixed in 6.9.4 with commit e8b485e39b4d
	Issue introduced in 5.17 with commit 1517c1a7a445 and fixed in 6.10-rc1 with commit 33e62cd7b4c2

Please see for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files

The file(s) affected by this issue are:


The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:

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