This is a note to let you know that I've just added the patch titled
f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()
to the 6.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
f2fs-fix-to-avoid-use-after-free-in-f2fs_stop_gc_thr.patch
and it can be found in the queue-6.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a7666572b8f81de5b425a552faf2549c794772be
Author: Chao Yu <chao@xxxxxxxxxx>
Date: Tue Jul 30 09:08:55 2024 +0800
f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()
[ Upstream commit c7f114d864ac91515bb07ac271e9824a20f5ed95 ]
syzbot reports a f2fs bug as below:
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
print_report+0xe8/0x550 mm/kasan/report.c:491
kasan_report+0x143/0x180 mm/kasan/report.c:601
kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
__refcount_add include/linux/refcount.h:184 [inline]
__refcount_inc include/linux/refcount.h:241 [inline]
refcount_inc include/linux/refcount.h:258 [inline]
get_task_struct include/linux/sched/task.h:118 [inline]
kthread_stop+0xca/0x630 kernel/kthread.c:704
f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
__f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
The root cause is below race condition, it may cause use-after-free
issue in sbi->gc_th pointer.
- remount
- f2fs_remount
- f2fs_stop_gc_thread
- kfree(gc_th)
- f2fs_ioc_shutdown
- f2fs_do_shutdown
- f2fs_stop_gc_thread
- kthread_stop(gc_th->f2fs_gc_task)
: sbi->gc_thread = NULL;
We will call f2fs_do_shutdown() in two paths:
- for f2fs_ioc_shutdown() path, we should grab sb->s_umount semaphore
for fixing.
- for f2fs_shutdown() path, it's safe since caller has already grabbed
sb->s_umount semaphore.
Reported-by: syzbot+1a8e2b31f2ac9bd3d148@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/linux-f2fs-devel/0000000000005c7ccb061e032b9b@xxxxxxxxxx
Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown")
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index eb6b3e62e6575..f4342622dec6a 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3503,7 +3503,7 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
int f2fs_truncate_hole(struct inode *inode, pgoff_t pg_start, pgoff_t pg_end);
void f2fs_truncate_data_blocks_range(struct dnode_of_data *dn, int count);
int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsigned int flag,
- bool readonly);
+ bool readonly, bool need_lock);
int f2fs_precache_extents(struct inode *inode);
int f2fs_fileattr_get(struct dentry *dentry, struct fileattr *fa);
int f2fs_fileattr_set(struct mnt_idmap *idmap,
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 5558a75f29b79..869f4744b443e 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2280,7 +2280,7 @@ static int f2fs_ioc_abort_atomic_write(struct file *filp)
}
int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsigned int flag,
- bool readonly)
+ bool readonly, bool need_lock)
{
struct super_block *sb = sbi->sb;
int ret = 0;
@@ -2327,12 +2327,19 @@ int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsigned int flag,
if (readonly)
goto out;
+ /* grab sb->s_umount to avoid racing w/ remount() */
+ if (need_lock)
+ down_read(&sbi->sb->s_umount);
+
f2fs_stop_gc_thread(sbi);
f2fs_stop_discard_thread(sbi);
f2fs_drop_discard_cmd(sbi);
clear_opt(sbi, DISCARD);
+ if (need_lock)
+ up_read(&sbi->sb->s_umount);
+
f2fs_update_time(sbi, REQ_TIME);
out:
@@ -2369,7 +2376,7 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
}
}
- ret = f2fs_do_shutdown(sbi, in, readonly);
+ ret = f2fs_do_shutdown(sbi, in, readonly, true);
if (need_drop)
mnt_drop_write_file(filp);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 3959fd137cc9b..4e46cbd1fc2ba 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2561,7 +2561,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
static void f2fs_shutdown(struct super_block *sb)
{
- f2fs_do_shutdown(F2FS_SB(sb), F2FS_GOING_DOWN_NOSYNC, false);
+ f2fs_do_shutdown(F2FS_SB(sb), F2FS_GOING_DOWN_NOSYNC, false, false);
}
#ifdef CONFIG_QUOTA
