CVE-2024-46687

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix a use-after-free when hitting errors inside btrfs_submit_chunk()

[BUG]

There is an internal report that KASAN is reporting use-after-free, with

the following backtrace:

BUG: KASAN: slab-use-after-free in btrfs_check_read_bio+0xa68/0xb70 [btrfs]

Read of size 4 at addr ffff8881117cec28 by task kworker/u16:2/45

CPU: 1 UID: 0 PID: 45 Comm: kworker/u16:2 Not tainted 6.11.0-rc2-next-20240805-default+ #76

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-3-gd478f380-rebuilt.opensuse.org 04/01/2014

Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]

Call Trace:

dump_stack_lvl+0x61/0x80

print_address_description.constprop.0+0x5e/0x2f0

print_report+0x118/0x216

kasan_report+0x11d/0x1f0

btrfs_check_read_bio+0xa68/0xb70 [btrfs]

process_one_work+0xce0/0x12a0

worker_thread+0x717/0x1250

kthread+0x2e3/0x3c0

ret_from_fork+0x2d/0x70

ret_from_fork_asm+0x11/0x20

Allocated by task 20917:

kasan_save_stack+0x37/0x60

kasan_save_track+0x10/0x30

__kasan_slab_alloc+0x7d/0x80

kmem_cache_alloc_noprof+0x16e/0x3e0

mempool_alloc_noprof+0x12e/0x310

bio_alloc_bioset+0x3f0/0x7a0

btrfs_bio_alloc+0x2e/0x50 [btrfs]

submit_extent_page+0x4d1/0xdb0 [btrfs]

btrfs_do_readpage+0x8b4/0x12a0 [btrfs]

btrfs_readahead+0x29a/0x430 [btrfs]

read_pages+0x1a7/0xc60

page_cache_ra_unbounded+0x2ad/0x560

filemap_get_pages+0x629/0xa20

filemap_read+0x335/0xbf0

vfs_read+0x790/0xcb0

ksys_read+0xfd/0x1d0

do_syscall_64+0x6d/0x140

entry_SYSCALL_64_after_hwframe+0x4b/0x53

Freed by task 20917:

kasan_save_stack+0x37/0x60

kasan_save_track+0x10/0x30

kasan_save_free_info+0x37/0x50

__kasan_slab_free+0x4b/0x60

kmem_cache_free+0x214/0x5d0

bio_free+0xed/0x180

end_bbio_data_read+0x1cc/0x580 [btrfs]

btrfs_submit_chunk+0x98d/0x1880 [btrfs]

btrfs_submit_bio+0x33/0x70 [btrfs]

submit_one_bio+0xd4/0x130 [btrfs]

submit_extent_page+0x3ea/0xdb0 [btrfs]

btrfs_do_readpage+0x8b4/0x12a0 [btrfs]

btrfs_readahead+0x29a/0x430 [btrfs]

read_pages+0x1a7/0xc60

page_cache_ra_unbounded+0x2ad/0x560

filemap_get_pages+0x629/0xa20

filemap_read+0x335/0xbf0

vfs_read+0x790/0xcb0

ksys_read+0xfd/0x1d0

do_syscall_64+0x6d/0x140

entry_SYSCALL_64_after_hwframe+0x4b/0x53

[CAUSE]

Although I cannot reproduce the error, the report itself is good enough

to pin down the cause.

The call trace is the regular endio workqueue context, but the

free-by-task trace is showing that during btrfs_submit_chunk() we

already hit a critical error, and is calling btrfs_bio_end_io() to error

out. And the original endio function called bio_put() to free the whole

bio.

This means a double freeing thus causing use-after-free, e.g.:

1. Enter btrfs_submit_bio() with a read bio

The read bio length is 128K, crossing two 64K stripes.

2. The first run of btrfs_submit_chunk()

2.1 Call btrfs_map_block(), which returns 64K

2.2 Call btrfs_split_bio()

Now there are two bios, one referring to the first 64K, the other

referring to the second 64K.

2.3 The first half is submitted.

3. The second run of btrfs_submit_chunk()

3.1 Call btrfs_map_block(), which by somehow failed

Now we call btrfs_bio_end_io() to handle the error

3.2 btrfs_bio_end_io() calls the original endio function

Which is end_bbio_data_read(), and it calls bio_put() for the

original bio.

Now the original bio is freed.

4. The submitted first 64K bio finished

Now we call into btrfs_check_read_bio() and tries to advance the bio

iter.

But since the original bio (thus its iter) is already freed, we

trigger the above use-after free.

And even if the memory is not poisoned/corrupted, we will later call

the original endio function, causing a double freeing.

[FIX]

Instead of calling btrfs_bio_end_io(), call btrfs_orig_bbio_end_io(),

which has the extra check on split bios and do the pr

---truncated---