CVE-2021-47508

In the Linux kernel, the following vulnerability has been resolved: btrfs:
free exchange changeset on failures Fstests runs on my VMs have show
several kmemleak reports like the following. unreferenced object
0xffff88811ae59080 (size 64): comm “xfs_io”, pid 12124, jiffies 4294987392
(age 6.368s) hex dump (first 32 bytes): 00 c0 1c 00 00 00 00 00 ff cf 1c 00
00 00 00 00 … 90 97 e5 1a 81 88 ff ff 90 97 e5 1a 81 88 ff
ff … backtrace: [<00000000ac0176d2>]
ulist_add_merge+0x60/0x150 [btrfs] [<0000000076e9f312>]
set_state_bits+0x86/0xc0 [btrfs] [<0000000014fe73d6>]
set_extent_bit+0x270/0x690 [btrfs] [<000000004f675208>]
set_record_extent_bits+0x19/0x20 [btrfs] [<00000000b96137b1>]
qgroup_reserve_data+0x274/0x310 [btrfs] [<0000000057e9dcbb>]
btrfs_check_data_free_space+0x5c/0xa0 [btrfs] [<0000000019c4511d>]
btrfs_delalloc_reserve_space+0x1b/0xa0 [btrfs] [<000000006d37e007>]
btrfs_dio_iomap_begin+0x415/0x970 [btrfs] [<00000000fb8a74b8>]
iomap_iter+0x161/0x1e0 [<0000000071dff6ff>] __iomap_dio_rw+0x1df/0x700
[<000000002567ba53>] iomap_dio_rw+0x5/0x20 [<0000000072e555f8>]
btrfs_file_write_iter+0x290/0x530 [btrfs] [<000000005eb3d845>]
new_sync_write+0x106/0x180 [<000000003fb505bf>] vfs_write+0x24d/0x2f0
[<000000009bb57d37>] __x64_sys_pwrite64+0x69/0xa0 [<000000003eba3fdf>]
do_syscall_64+0x43/0x90 In case brtfs_qgroup_reserve_data() or
btrfs_delalloc_reserve_metadata() fail the allocated extent_changeset will
not be freed. So in btrfs_check_data_free_space() and
btrfs_delalloc_reserve_space() free the allocated extent_changeset to get
rid of the allocated memory. The issue currently only happens in the direct
IO write path, but only after 65b3c08606e5 (“btrfs: fix ENOSPC failure when
attempting direct IO write into NOCOW range”), and also at
defrag_one_locked_target(). Every other place is always calling
extent_changeset_free() even if its call to btrfs_delalloc_reserve_space()
or btrfs_check_data_free_space() has failed.