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Youzhong Yang 167cbd3e52 nfsd: add list_head nf_gc to struct nfsd_file 
commit 8e6e2ffa65 upstream.

nfsd_file_put() in one thread can race with another thread doing
garbage collection (running nfsd_file_gc() -> list_lru_walk() ->
nfsd_file_lru_cb()):

  * In nfsd_file_put(), nf->nf_ref is 1, so it tries to do nfsd_file_lru_add().
  * nfsd_file_lru_add() returns true (with NFSD_FILE_REFERENCED bit set)
  * garbage collector kicks in, nfsd_file_lru_cb() clears REFERENCED bit and
    returns LRU_ROTATE.
  * garbage collector kicks in again, nfsd_file_lru_cb() now decrements nf->nf_ref
    to 0, runs nfsd_file_unhash(), removes it from the LRU and adds to the dispose
    list [list_lru_isolate_move(lru, &nf->nf_lru, head)]
  * nfsd_file_put() detects NFSD_FILE_HASHED bit is cleared, so it tries to remove
    the 'nf' from the LRU [if (!nfsd_file_lru_remove(nf))]. The 'nf' has been added
    to the 'dispose' list by nfsd_file_lru_cb(), so nfsd_file_lru_remove(nf) simply
    treats it as part of the LRU and removes it, which leads to its removal from
    the 'dispose' list.
  * At this moment, 'nf' is unhashed with its nf_ref being 0, and not on the LRU.
    nfsd_file_put() continues its execution [if (refcount_dec_and_test(&nf->nf_ref))],
    as nf->nf_ref is already 0, nf->nf_ref is set to REFCOUNT_SATURATED, and the 'nf'
    gets no chance of being freed.

nfsd_file_put() can also race with nfsd_file_cond_queue():
  * In nfsd_file_put(), nf->nf_ref is 1, so it tries to do nfsd_file_lru_add().
  * nfsd_file_lru_add() sets REFERENCED bit and returns true.
  * Some userland application runs 'exportfs -f' or something like that, which triggers
    __nfsd_file_cache_purge() -> nfsd_file_cond_queue().
  * In nfsd_file_cond_queue(), it runs [if (!nfsd_file_unhash(nf))], unhash is done
    successfully.
  * nfsd_file_cond_queue() runs [if (!nfsd_file_get(nf))], now nf->nf_ref goes to 2.
  * nfsd_file_cond_queue() runs [if (nfsd_file_lru_remove(nf))], it succeeds.
  * nfsd_file_cond_queue() runs [if (refcount_sub_and_test(decrement, &nf->nf_ref))]
    (with "decrement" being 2), so the nf->nf_ref goes to 0, the 'nf' is added to the
    dispose list [list_add(&nf->nf_lru, dispose)]
  * nfsd_file_put() detects NFSD_FILE_HASHED bit is cleared, so it tries to remove
    the 'nf' from the LRU [if (!nfsd_file_lru_remove(nf))], although the 'nf' is not
    in the LRU, but it is linked in the 'dispose' list, nfsd_file_lru_remove() simply
    treats it as part of the LRU and removes it. This leads to its removal from
    the 'dispose' list!
  * Now nf->ref is 0, unhashed. nfsd_file_put() continues its execution and set
    nf->nf_ref to REFCOUNT_SATURATED.

As shown in the above analysis, using nf_lru for both the LRU list and dispose list
can cause the leaks. This patch adds a new list_head nf_gc in struct nfsd_file, and uses
it for the dispose list. This does not fix the nfsd_file leaking issue completely.

Signed-off-by: Youzhong Yang <youzhong@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-01-23 17:16:03 +01:00
arch x86/asm: Make serialize() always_inline 2025-01-23 17:16:01 +01:00
block block, bfq: fix waker_bfqq UAF after bfq_split_bfqq() 2025-01-23 17:15:55 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: pcrypt - Call crypto layer directly when padata_do_parallel() return -EBUSY 2024-12-14 19:50:44 +01:00
Documentation dt-bindings: display: adi,adv7533: Drop single lane support 2025-01-09 13:28:50 +01:00
drivers Revert "regmap: detach regmap from dev on regmap_exit" 2025-01-23 17:16:03 +01:00
fs nfsd: add list_head nf_gc to struct nfsd_file 2025-01-23 17:16:03 +01:00
include blk-cgroup: Fix UAF in blkcg_unpin_online() 2025-01-23 17:16:03 +01:00
init initramfs: avoid filename buffer overrun 2024-12-14 19:50:42 +01:00
io_uring io_uring: fix possible deadlock in io_register_iowq_max_workers() 2024-11-17 15:06:25 +01:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel hrtimers: Handle CPU state correctly on hotplug 2025-01-23 17:16:02 +01:00
lib lib: stackinit: hide never-taken branch from compiler 2025-01-09 13:28:41 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm filemap: avoid truncating 64-bit offset to 32 bits 2025-01-23 17:16:01 +01:00
net ipv6: avoid possible NULL deref in rt6_uncached_list_flush_dev() 2025-01-23 17:16:03 +01:00
samples samples/bpf: Fix a resource leak 2024-12-14 19:51:36 +01:00
scripts scripts/sorttable: fix orc_sort_cmp() to maintain symmetry and transitivity 2025-01-23 17:15:52 +01:00
security selinux: ignore unknown extended permissions 2025-01-09 13:28:42 +01:00
sound ASoC: mediatek: disable buffer pre-allocation 2025-01-23 17:15:49 +01:00
tools objtool/x86: allow syscall instruction 2024-12-19 18:07:22 +01:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-10-22 15:40:41 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS trace: Relocate event helper files 2024-04-10 16:19:24 +02:00
Makefile Linux 5.15.176 2025-01-09 13:28:51 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.