CVE-2024-26644

In the Linux kernel, the following vulnerability has been resolved: btrfs:
don’t abort filesystem when attempting to snapshot deleted subvolume If the
source file descriptor to the snapshot ioctl refers to a deleted subvolume,
we get the following abort: BTRFS: Transaction aborted (error -2) WARNING:
CPU: 0 PID: 833 at fs/btrfs/transaction.c:1875
create_pending_snapshot+0x1040/0x1190 [btrfs] Modules linked in: pata_acpi
btrfs ata_piix libata scsi_mod virtio_net blake2b_generic xor net_failover
virtio_rng failover scsi_common rng_core raid6_pq libcrc32c CPU: 0 PID: 833
Comm: t_snapshot_dele Not tainted 6.7.0-rc6 #2 Hardware name: QEMU Standard
PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014 RIP:
0010:create_pending_snapshot+0x1040/0x1190 [btrfs] RSP:
0018:ffffa09c01337af8 EFLAGS: 00010282 RAX: 0000000000000000 RBX:
ffff9982053e7c78 RCX: 0000000000000027 RDX: ffff99827dc20848 RSI:
0000000000000001 RDI: ffff99827dc20840 RBP: ffffa09c01337c00 R08:
0000000000000000 R09: ffffa09c01337998 R10: 0000000000000003 R11:
ffffffffb96da248 R12: fffffffffffffffe R13: ffff99820535bb28 R14:
ffff99820b7bd000 R15: ffff99820381ea80 FS: 00007fe20aadabc0(0000)
GS:ffff99827dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000
CR0: 0000000080050033 CR2: 0000559a120b502f CR3: 00000000055b6000 CR4:
00000000000006f0 Call Trace: <TASK> ? create_pending_snapshot+0x1040/0x1190
[btrfs] ? __warn+0x81/0x130 ? create_pending_snapshot+0x1040/0x1190 [btrfs]
? report_bug+0x171/0x1a0 ? handle_bug+0x3a/0x70 ? exc_invalid_op+0x17/0x70
? asm_exc_invalid_op+0x1a/0x20 ? create_pending_snapshot+0x1040/0x1190
[btrfs] ? create_pending_snapshot+0x1040/0x1190 [btrfs]
create_pending_snapshots+0x92/0xc0 [btrfs]
btrfs_commit_transaction+0x66b/0xf40 [btrfs] btrfs_mksubvol+0x301/0x4d0
[btrfs] btrfs_mksnapshot+0x80/0xb0 [btrfs]
__btrfs_ioctl_snap_create+0x1c2/0x1d0 [btrfs]
btrfs_ioctl_snap_create_v2+0xc4/0x150 [btrfs] btrfs_ioctl+0x8a6/0x2650
[btrfs] ? kmem_cache_free+0x22/0x340 ? do_sys_openat2+0x97/0xe0
__x64_sys_ioctl+0x97/0xd0 do_syscall_64+0x46/0xf0
entry_SYSCALL_64_after_hwframe+0x6e/0x76 RIP: 0033:0x7fe20abe83af RSP:
002b:00007ffe6eff1360 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX:
ffffffffffffffda RBX: 0000000000000004 RCX: 00007fe20abe83af RDX:
00007ffe6eff23c0 RSI: 0000000050009417 RDI: 0000000000000003 RBP:
0000000000000003 R08: 0000000000000000 R09: 00007fe20ad16cd0 R10:
0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13:
00007ffe6eff13c0 R14: 00007fe20ad45000 R15: 0000559a120b6d58 </TASK> —[
end trace 0000000000000000 ]— BTRFS: error (device vdc: state A) in
create_pending_snapshot:1875: errno=-2 No such entry BTRFS info (device
vdc: state EA): forced readonly BTRFS warning (device vdc: state EA):
Skipping commit of aborted transaction. BTRFS: error (device vdc: state EA)
in cleanup_transaction:2055: errno=-2 No such entry This happens because
create_pending_snapshot() initializes the new root item as a copy of the
source root item. This includes the refs field, which is 0 for a deleted
subvolume. The call to btrfs_insert_root() therefore inserts a root with
refs == 0. btrfs_get_new_fs_root() then finds the root and returns -ENOENT
if refs == 0, which causes create_pending_snapshot() to abort. Fix it by
checking the source root’s refs before attempting the snapshot, but after
locking subvol_sem to avoid racing with deletion.

Notes