Following process will trigger an infinite loop in ubi_wl_put_peb():
ubifs_bgt ubi_bgt
ubifs_leb_unmap
ubi_leb_unmap
ubi_eba_unmap_leb
ubi_wl_put_peb wear_leveling_worker
e1 = rb_entry(rb_first(&ubi->used)
e2 = get_peb_for_wl(ubi)
ubi_io_read_vid_hdr // return err (flash fault)
out_error:
ubi->move_from = ubi->move_to = NULL
wl_entry_destroy(ubi, e1)
ubi->lookuptbl[e->pnum] = NULL
retry:
e = ubi->lookuptbl[pnum]; // return NULL
if (e == ubi->move_from) { // NULL == NULL gets true
goto retry; // infinite loop !!!
$ top
PID USER PR NI VIRT RES SHR S %CPU %MEM COMMAND
7676 root 20 0 0 0 0 R 100.0 0.0 ubifs_bgt0_0
Fix it by:
1) Letting ubi_wl_put_peb() returns directly if wearl leveling entry has
been removed from 'ubi->lookuptbl'.
2) Using 'ubi->wl_lock' protecting wl entry deletion to preventing an
use-after-free problem for wl entry in ubi_wl_put_peb().
Fetch a reproducer in [Link].
Fixes: 43f9b25a9cdd7b1 ("UBI: bugfix: protect from volume removal")
Fixes: ee59ba8b064f692 ("UBI: Fix stale pointers in ubi->lookuptbl")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216111
Signed-off-by: Zhihao Cheng <[email protected]>
---
v1->v2: Don't split wl_entry_destroy(), since kmem_cache_free() can be
executed wrapped a spinlock, eg dtl_disable().
drivers/mtd/ubi/wl.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 55bae06cf408..ee0100740869 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -973,11 +973,11 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
spin_lock(&ubi->wl_lock);
ubi->move_from = ubi->move_to = NULL;
ubi->move_to_put = ubi->wl_scheduled = 0;
+ wl_entry_destroy(ubi, e1);
+ wl_entry_destroy(ubi, e2);
spin_unlock(&ubi->wl_lock);
ubi_free_vid_buf(vidb);
- wl_entry_destroy(ubi, e1);
- wl_entry_destroy(ubi, e2);
out_ro:
ubi_ro_mode(ubi);
@@ -1253,6 +1253,18 @@ int ubi_wl_put_peb(struct ubi_device *ubi, int vol_id, int lnum,
retry:
spin_lock(&ubi->wl_lock);
e = ubi->lookuptbl[pnum];
+ if (!e) {
+ /*
+ * This wl entry has been removed for some errors by other
+ * process (eg. wear leveling worker), corresponding process
+ * (except __erase_worker, which cannot concurrent with
+ * ubi_wl_put_peb) will set ubi ro_mode at the same time,
+ * just ignore this wl entry.
+ */
+ spin_unlock(&ubi->wl_lock);
+ up_read(&ubi->fm_protect);
+ return 0;
+ }
if (e == ubi->move_from) {
/*
* User is putting the physical eraseblock which was selected to
--
2.31.1