[PATCH 5.15 090/121] erofs: fix pcluster use-after-free on UP platforms

Greg Kroah-Hartman
2022-09-13T14:40:53Z

From: Gao Xiang <hsiangkao@linux.alibaba.com>

[ Upstream commit 2f44013e39984c127c6efedf70e6b5f4e9dcf315 ]

During stress testing with CONFIG_SMP disabled, KASAN reports as below:

==================================================================
BUG: KASAN: use-after-free in __mutex_lock+0xe5/0xc30
Read of size 8 at addr ffff8881094223f8 by task stress/7789

CPU: 0 PID: 7789 Comm: stress Not tainted 6.0.0-rc1-00002-g0d53d2e882f9 #3
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
Call Trace:
<TASK>
..
__mutex_lock+0xe5/0xc30
..
z_erofs_do_read_page+0x8ce/0x1560
..
z_erofs_readahead+0x31c/0x580
..
Freed by task 7787
kasan_save_stack+0x1e/0x40
kasan_set_track+0x20/0x30
kasan_set_free_info+0x20/0x40
__kasan_slab_free+0x10c/0x190
kmem_cache_free+0xed/0x380
rcu_core+0x3d5/0xc90
__do_softirq+0x12d/0x389

Last potentially related work creation:
kasan_save_stack+0x1e/0x40
__kasan_record_aux_stack+0x97/0xb0
call_rcu+0x3d/0x3f0
erofs_shrink_workstation+0x11f/0x210
erofs_shrink_scan+0xdc/0x170
shrink_slab.constprop.0+0x296/0x530
drop_slab+0x1c/0x70
drop_caches_sysctl_handler+0x70/0x80
proc_sys_call_handler+0x20a/0x2f0
vfs_write+0x555/0x6c0
ksys_write+0xbe/0x160
do_syscall_64+0x3b/0x90

The root cause is that erofs_workgroup_unfreeze() doesn't reset to
orig_val thus it causes a race that the pcluster reuses unexpectedly
before freeing.

Since UP platforms are quite rare now, such path becomes unnecessary.
Let's drop such specific-designed path directly instead.

Fixes: 73f5c66df3e2 ("staging: erofs: fix `erofs_workgroup_{try_to_freeze, unfreeze}'")
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20220902045710.109530-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/erofs/internal.h | 29 -----------------------------
1 file changed, 29 deletions(-)

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 9524e155b38fa..b77acf09726c6 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -143,7 +143,6 @@ struct erofs_workgroup {
atomic_t refcount;
};

-#if defined(CONFIG_SMP)
static inline bool erofs_workgroup_try_to_freeze(struct erofs_workgroup *grp,
int val)
{
@@ -172,34 +171,6 @@ static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
return atomic_cond_read_relaxed(&grp->refcount,
VAL != EROFS_LOCKED_MAGIC);
}
-#else
-static inline bool erofs_workgroup_try_to_freeze(struct erofs_workgroup *grp,
- int val)
-{
- preempt_disable();
- /* no need to spin on UP platforms, let's just disable preemption. */
- if (val != atomic_read(&grp->refcount)) {
- preempt_enable();
- return false;
- }
- return true;
-}
-
-static inline void erofs_workgroup_unfreeze(struct erofs_workgroup *grp,
- int orig_val)
-{
- preempt_enable();
-}
-
-static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
-{
- int v = atomic_read(&grp->refcount);
-
- /* workgroup is never freezed on uniprocessor systems */
- DBG_BUGON(v == EROFS_LOCKED_MAGIC);
- return v;
-}
-#endif /* !CONFIG_SMP */
#endif /* !CONFIG_EROFS_FS_ZIP */

/* we strictly follow PAGE_SIZE and no buffer head yet */
--
2.35.1