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btrfs: scrub: avoid use-after-free when chunk length is not 64K aligned

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commit f546c42826 upstream.

[BUG]
There is a bug report that, on a ext4-converted btrfs, scrub leads to
various problems, including:

- "unable to find chunk map" errors
  BTRFS info (device vdb): scrub: started on devid 1
  BTRFS critical (device vdb): unable to find chunk map for logical 2214744064 length 4096
  BTRFS critical (device vdb): unable to find chunk map for logical 2214744064 length 45056

  This would lead to unrepariable errors.

- Use-after-free KASAN reports:
  ==================================================================
  BUG: KASAN: slab-use-after-free in __blk_rq_map_sg+0x18f/0x7c0
  Read of size 8 at addr ffff8881013c9040 by task btrfs/909
  CPU: 0 PID: 909 Comm: btrfs Not tainted 6.7.0-x64v3-dbg #11 c50636e9419a8354555555245df535e380563b2b
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 2023.11-2 12/24/2023
  Call Trace:
   <TASK>
   dump_stack_lvl+0x43/0x60
   print_report+0xcf/0x640
   kasan_report+0xa6/0xd0
   __blk_rq_map_sg+0x18f/0x7c0
   virtblk_prep_rq.isra.0+0x215/0x6a0 [virtio_blk 19a65eeee9ae6fcf02edfad39bb9ddee07dcdaff]
   virtio_queue_rqs+0xc4/0x310 [virtio_blk 19a65eeee9ae6fcf02edfad39bb9ddee07dcdaff]
   blk_mq_flush_plug_list.part.0+0x780/0x860
   __blk_flush_plug+0x1ba/0x220
   blk_finish_plug+0x3b/0x60
   submit_initial_group_read+0x10a/0x290 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
   flush_scrub_stripes+0x38e/0x430 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
   scrub_stripe+0x82a/0xae0 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
   scrub_chunk+0x178/0x200 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
   scrub_enumerate_chunks+0x4bc/0xa30 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
   btrfs_scrub_dev+0x398/0x810 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
   btrfs_ioctl+0x4b9/0x3020 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
   __x64_sys_ioctl+0xbd/0x100
   do_syscall_64+0x5d/0xe0
   entry_SYSCALL_64_after_hwframe+0x63/0x6b
  RIP: 0033:0x7f47e5e0952b

- Crash, mostly due to above use-after-free

[CAUSE]
The converted fs has the following data chunk layout:

    item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 2214658048) itemoff 16025 itemsize 80
        length 86016 owner 2 stripe_len 65536 type DATA|single

For above logical bytenr 2214744064, it's at the chunk end
(2214658048 + 86016 = 2214744064).

This means btrfs_submit_bio() would split the bio, and trigger endio
function for both of the two halves.

However scrub_submit_initial_read() would only expect the endio function
to be called once, not any more.
This means the first endio function would already free the bbio::bio,
leaving the bvec freed, thus the 2nd endio call would lead to
use-after-free.

[FIX]
- Make sure scrub_read_endio() only updates bits in its range
  Since we may read less than 64K at the end of the chunk, we should not
  touch the bits beyond chunk boundary.

- Make sure scrub_submit_initial_read() only to read the chunk range
  This is done by calculating the real number of sectors we need to
  read, and add sector-by-sector to the bio.

Thankfully the scrub read repair path won't need extra fixes:

- scrub_stripe_submit_repair_read()
  With above fixes, we won't update error bit for range beyond chunk,
  thus scrub_stripe_submit_repair_read() should never submit any read
  beyond the chunk.

Reported-by: Rongrong <i@rong.moe>
Fixes: e02ee89baa ("btrfs: scrub: switch scrub_simple_mirror() to scrub_stripe infrastructure")
Tested-by: Rongrong <i@rong.moe>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[ Use min_t() to fix a compiling error due to difference types ]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Qu Wenruo 2024-01-17 11:02:25 +10:30 committed by Greg Kroah-Hartman
parent d60ff1d313
commit 642b9c520e
1 changed files with 22 additions and 7 deletions
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29
fs/btrfs/scrub.c
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@ -1099,12 +1099,22 @@ static void scrub_stripe_read_repair_worker(struct work_struct *work)
static void scrub_read_endio(struct btrfs_bio *bbio)
{
struct scrub_stripe *stripe = bbio->private;
struct bio_vec *bvec;
int sector_nr = calc_sector_number(stripe, bio_first_bvec_all(&bbio->bio));
int num_sectors;
u32 bio_size = 0;
int i;
ASSERT(sector_nr < stripe->nr_sectors);
bio_for_each_bvec_all(bvec, &bbio->bio, i)
bio_size += bvec->bv_len;
num_sectors = bio_size >> stripe->bg->fs_info->sectorsize_bits;
if (bbio->bio.bi_status) {
bitmap_set(&stripe->io_error_bitmap, 0, stripe->nr_sectors);
bitmap_set(&stripe->error_bitmap, 0, stripe->nr_sectors);
bitmap_set(&stripe->io_error_bitmap, sector_nr, num_sectors);
bitmap_set(&stripe->error_bitmap, sector_nr, num_sectors);
} else {
bitmap_clear(&stripe->io_error_bitmap, 0, stripe->nr_sectors);
bitmap_clear(&stripe->io_error_bitmap, sector_nr, num_sectors);
}
bio_put(&bbio->bio);
if (atomic_dec_and_test(&stripe->pending_io)) {
@ -1640,6 +1650,9 @@ static void scrub_submit_initial_read(struct scrub_ctx *sctx,
{
struct btrfs_fs_info *fs_info = sctx->fs_info;
struct btrfs_bio *bbio;
unsigned int nr_sectors = min_t(u64, BTRFS_STRIPE_LEN, stripe->bg->start +
stripe->bg->length - stripe->logical) >>
fs_info->sectorsize_bits;
int mirror = stripe->mirror_num;
ASSERT(stripe->bg);
@ -1649,14 +1662,16 @@ static void scrub_submit_initial_read(struct scrub_ctx *sctx,
bbio = btrfs_bio_alloc(SCRUB_STRIPE_PAGES, REQ_OP_READ, fs_info,
scrub_read_endio, stripe);
/* Read the whole stripe. */
bbio->bio.bi_iter.bi_sector = stripe->logical >> SECTOR_SHIFT;
for (int i = 0; i < BTRFS_STRIPE_LEN >> PAGE_SHIFT; i++) {
/* Read the whole range inside the chunk boundary. */
for (unsigned int cur = 0; cur < nr_sectors; cur++) {
struct page *page = scrub_stripe_get_page(stripe, cur);
unsigned int pgoff = scrub_stripe_get_page_offset(stripe, cur);
int ret;
ret = bio_add_page(&bbio->bio, stripe->pages[i], PAGE_SIZE, 0);
ret = bio_add_page(&bbio->bio, page, fs_info->sectorsize, pgoff);
/* We should have allocated enough bio vectors. */
ASSERT(ret == PAGE_SIZE);
ASSERT(ret == fs_info->sectorsize);
}
atomic_inc(&stripe->pending_io);