6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chao Yu <chao@xxxxxxxxxx> [ 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> --- fs/f2fs/f2fs.h | 2 +- fs/f2fs/file.c | 11 +++++++++-- fs/f2fs/super.c | 2 +- 3 files changed, 11 insertions(+), 4 deletions(-) diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h index 2059a24a330b2..6c9b1759f4e74 100644 --- a/fs/f2fs/f2fs.h +++ b/fs/f2fs/f2fs.h @@ -3508,7 +3508,7 @@ 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 085008b208020..0c279ba451205 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -2257,7 +2257,7 @@ 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; @@ -2299,12 +2299,19 @@ 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: @@ -2341,7 +2348,7 @@ 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 d12603c3b5f50..2bec5176df65d 100644 --- a/fs/f2fs/super.c +++ b/fs/f2fs/super.c @@ -2545,7 +2545,7 @@ 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 -- 2.43.0
