CVE-2024-26616

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

Notes