This is a note to let you know that I've just added the patch titled
btrfs: scrub: avoid use-after-free when chunk length is not 64K aligned
to the 6.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-scrub-avoid-use-after-free-when-chunk-length-i.patch
and it can be found in the queue-6.7 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7893c91364a20cba4d0c74f3b3455ab5e3175dec
Author: Qu Wenruo <wqu@xxxxxxxx>
Date: Wed Jan 17 11:02:25 2024 +1030
btrfs: scrub: avoid use-after-free when chunk length is not 64K aligned
[ Upstream commit f546c4282673497a06ecb6190b50ae7f6c85b02f ]
[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@xxxxxxxx>
Fixes: e02ee89baa66 ("btrfs: scrub: switch scrub_simple_mirror() to scrub_stripe infrastructure")
Tested-by: Rongrong <i@xxxxxxxx>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index f62a408671cb..443d2519f0a9 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -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)) {
@@ -1705,6 +1715,9 @@ 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(BTRFS_STRIPE_LEN, stripe->bg->start +
+ stripe->bg->length - stripe->logical) >>
+ fs_info->sectorsize_bits;
int mirror = stripe->mirror_num;
ASSERT(stripe->bg);
@@ -1719,14 +1732,16 @@ 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);
