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Qu Wenruo aee5f69f3e btrfs: avoid NULL pointer dereference if no valid extent tree 
[ Upstream commit 6aecd91a5c ]

[BUG]
Syzbot reported a crash with the following call trace:

  BTRFS info (device loop0): scrub: started on devid 1
  BUG: kernel NULL pointer dereference, address: 0000000000000208
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 106e70067 P4D 106e70067 PUD 107143067 PMD 0
  Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
  CPU: 1 UID: 0 PID: 689 Comm: repro Kdump: loaded Tainted: G           O       6.13.0-rc4-custom+ #206
  Tainted: [O]=OOT_MODULE
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022
  RIP: 0010:find_first_extent_item+0x26/0x1f0 [btrfs]
  Call Trace:
   <TASK>
   scrub_find_fill_first_stripe+0x13d/0x3b0 [btrfs]
   scrub_simple_mirror+0x175/0x260 [btrfs]
   scrub_stripe+0x5d4/0x6c0 [btrfs]
   scrub_chunk+0xbb/0x170 [btrfs]
   scrub_enumerate_chunks+0x2f4/0x5f0 [btrfs]
   btrfs_scrub_dev+0x240/0x600 [btrfs]
   btrfs_ioctl+0x1dc8/0x2fa0 [btrfs]
   ? do_sys_openat2+0xa5/0xf0
   __x64_sys_ioctl+0x97/0xc0
   do_syscall_64+0x4f/0x120
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
   </TASK>

[CAUSE]
The reproducer is using a corrupted image where extent tree root is
corrupted, thus forcing to use "rescue=all,ro" mount option to mount the
image.

Then it triggered a scrub, but since scrub relies on extent tree to find
where the data/metadata extents are, scrub_find_fill_first_stripe()
relies on an non-empty extent root.

But unfortunately scrub_find_fill_first_stripe() doesn't really expect
an NULL pointer for extent root, it use extent_root to grab fs_info and
triggered a NULL pointer dereference.

[FIX]
Add an extra check for a valid extent root at the beginning of
scrub_find_fill_first_stripe().

The new error path is introduced by 42437a6386 ("btrfs: introduce
mount option rescue=ignorebadroots"), but that's pretty old, and later
commit b979547513 ("btrfs: scrub: introduce helper to find and fill
sector info for a scrub_stripe") changed how we do scrub.

So for kernels older than 6.6, the fix will need manual backport.

Reported-by: syzbot+339e9dbe3a2ca419b85d@syzkaller.appspotmail.com
Link: https://lore.kernel.org/linux-btrfs/67756935.050a0220.25abdd.0a12.GAE@google.com/
Fixes: 42437a6386 ("btrfs: introduce mount option rescue=ignorebadroots")
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-01-17 13:40:37 +01:00
arch ARC: build: Try to guess GCC variant of cross compiler 2025-01-09 13:33:47 +01:00
block block: lift bio_is_zone_append to bio.h 2025-01-09 13:33:32 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: ecdsa - Avoid signed integer overflow on signature decoding 2024-12-14 20:03:36 +01:00
Documentation fs/writeback: convert wbc_account_cgroup_owner to take a folio 2025-01-17 13:40:33 +01:00
drivers net: libwx: fix firmware mailbox abnormal return 2025-01-17 13:40:37 +01:00
fs btrfs: avoid NULL pointer dereference if no valid extent tree 2025-01-17 13:40:37 +01:00
include tcp/dccp: allow a connection when sk_max_ack_backlog is zero 2025-01-17 13:40:37 +01:00
init Compiler Attributes: disable __counted_by for clang < 19.1.3 2024-12-05 14:02:45 +01:00
io_uring io_uring/rw: fix downgraded mshot read 2025-01-09 13:33:51 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel fgraph: Add READ_ONCE() when accessing fgraph_array[] 2025-01-09 13:33:52 +01:00
lib maple_tree: reload mas before the second call for mas_empty_area 2025-01-09 13:33:50 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: hugetlb: independent PMD page table shared count 2025-01-09 13:33:54 +01:00
net net_sched: cls_flow: validate TCA_FLOW_RSHIFT attribute 2025-01-17 13:40:37 +01:00
rust rust: kbuild: set bindgen's Rust target version 2024-12-19 18:13:22 +01:00
samples samples/bpf: Fix a resource leak 2024-12-14 20:03:46 +01:00
scripts scripts/sorttable: fix orc_sort_cmp() to maintain symmetry and transitivity 2025-01-09 13:33:50 +01:00
security selinux: ignore unknown extended permissions 2025-01-09 13:33:32 +01:00
sound ASoC: mediatek: disable buffer pre-allocation 2025-01-17 13:40:36 +01:00
tools selftests/alsa: Fix circular dependency involving global-timer 2025-01-17 13:40:36 +01:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: switch hugepage recovery thread to vhost_task 2024-12-05 14:02:43 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Kbuild updates for v6.12 2024-09-24 13:02:06 -07:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: update location of media main tree 2024-12-05 14:02:42 +01:00
Makefile Linux 6.12.9 2025-01-09 13:33:55 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.