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The one_time_gc field in struct victim_sel_policy is conditionally
initialized but unconditionally read, leading to undefined behavior
that triggers UBSAN warnings.
In f2fs_get_victim() at fs/f2fs/gc.c:774, the victim_sel_policy
structure is declared without initialization:
struct victim_sel_policy p;
The field p.one_time_gc is only assigned when the 'one_time' parameter
is true (line 789):
if (one_time) {
p.one_time_gc = one_time;
...
}
However, this field is unconditionally read in subsequent get_gc_cost()
at line 395:
if (p->one_time_gc && (valid_thresh_ratio < 100) && ...)
When one_time is false, p.one_time_gc contains uninitialized stack
memory. Hence p.one_time_gc is an invalid bool value.
UBSAN detects this invalid bool value:
UBSAN: invalid-load in fs/f2fs/gc.c:395:7
load of value 77 is not a valid value for type '_Bool'
CPU: 3 UID: 0 PID: 1297 Comm: f2fs_gc-252:16 Not tainted 6.18.0-rc3
#5 PREEMPT(voluntary)
Hardware name: OpenStack Foundation OpenStack Nova,
BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x70/0x90
dump_stack+0x14/0x20
__ubsan_handle_load_invalid_value+0xb3/0xf0
? dl_server_update+0x2e/0x40
? update_curr+0x147/0x170
f2fs_get_victim.cold+0x66/0x134 [f2fs]
? sched_balance_newidle+0x2ca/0x470
? finish_task_switch.isra.0+0x8d/0x2a0
f2fs_gc+0x2ba/0x8e0 [f2fs]
? _raw_spin_unlock_irqrestore+0x12/0x40
? __timer_delete_sync+0x80/0xe0
? timer_delete_sync+0x14/0x20
? schedule_timeout+0x82/0x100
gc_thread_func+0x38b/0x860 [f2fs]
? gc_thread_func+0x38b/0x860 [f2fs]
? __pfx_autoremove_wake_function+0x10/0x10
kthread+0x10b/0x220
? __pfx_gc_thread_func+0x10/0x10 [f2fs]
? _raw_spin_unlock_irq+0x12/0x40
? __pfx_kthread+0x10/0x10
ret_from_fork+0x11a/0x160
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
This issue is reliably reproducible with the following steps on a
100GB SSD /dev/vdb:
mkfs.f2fs -f /dev/vdb
mount /dev/vdb /mnt/f2fs_test
fio --name=gc --directory=/mnt/f2fs_test --rw=randwrite \
--bs=4k --size=8G --numjobs=12 --fsync=4 --runtime=10 \
--time_based
echo 1 > /sys/fs/f2fs/vdb/gc_urgent
The uninitialized value causes incorrect GC victim selection, leading
to unpredictable garbage collection behavior.
Fix by zero-initializing the entire victim_sel_policy structure to
ensure all fields have defined values.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.