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Zhihao Cheng 5af1c64318 ubi: ubi_wl_put_peb: Fix infinite loop when wear-leveling work failed 
[ Upstream commit 4d57a7333e ]

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: 43f9b25a9c ("UBI: bugfix: protect from volume removal")
Fixes: ee59ba8b06 ("UBI: Fix stale pointers in ubi->lookuptbl")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216111
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2023-03-11 13:50:26 +01:00
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README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.