FAILED: patch "[PATCH] btrfs: scrub: avoid use-after-free when chunk length is not" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x f546c4282673497a06ecb6190b50ae7f6c85b02f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024012740-mating-boxing-dd93@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

f546c4282673 ("btrfs: scrub: avoid use-after-free when chunk length is not 64K aligned")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f546c4282673497a06ecb6190b50ae7f6c85b02f Mon Sep 17 00:00:00 2001
From: Qu Wenruo <[email protected]>
Date: Wed, 17 Jan 2024 11:02:25 +1030
Subject: [PATCH] btrfs: scrub: avoid use-after-free when chunk length is not
64K aligned

[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.

index a01807cbd4d4..2d81b1a18a04 100644
@@ -1098,12 +1098,22 @@ 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)) {

@@ -1701,6 +1711,9 @@ 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);

@@ -1715,14 +1728,16 @@ 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);
 

Great new hints on the conflict resolve steps, especially for guys like me, who is not familiar with stable kernels.

Would backport it soon.

Thanks,
Qu

[ 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.

---
 fs/btrfs/scrub.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

index 4445a52a0707..1e3ff87d0447 100644
@@ -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);
 

2.43.0

Now queued up, thanks!

greg k-h