[PATCH 6.12 208/567] f2fs: fix uninitialized one_time_gc in victim_sel_policy

Greg Kroah-Hartman
2026-01-06T17:26:07Z

From: Xiaole He <hexiaole1994@126.com>

commit 392711ef18bff524a873b9c239a73148c5432262 upstream.

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: e791d00bd06c ("f2fs: add valid block ratio not to do excessive GC for one time GC")
Cc: stable@kernel.org
Signed-off-by: Xiaole He <hexiaole1994@126.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/f2fs/gc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -787,7 +787,7 @@ int f2fs_get_victim(struct f2fs_sb_info
{
struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
struct sit_info *sm = SIT_I(sbi);
- struct victim_sel_policy p;
+ struct victim_sel_policy p = {0};
unsigned int secno, last_victim;
unsigned int last_segment;
unsigned int nsearched;