2024-04-04 08:20:23
Linux
PUBLISHED
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix double free of anonymous device after snapshot creation failure
When creating a snapshot we may do a double free of an anonymous device
in case theres an error committing the transaction. The second free may
result in freeing an anonymous device number that was allocated by some
other subsystem in the kernel or another btrfs filesystem.
The steps that lead to this:
1) At ioctl.c:create_snapshot() we allocate an anonymous device number
and assign it to pending_snapshot->anon_dev;
2) Then we call btrfs_commit_transaction() and end up at
transaction.c:create_pending_snapshot();
3) There we call btrfs_get_new_fs_root() and pass it the anonymous device
number stored in pending_snapshot->anon_dev;
4) btrfs_get_new_fs_root() frees that anonymous device number because
btrfs_lookup_fs_root() returned a root - someone else did a lookup
of the new root already, which could some task doing backref walking;
5) After that some error happens in the transaction commit path, and at
ioctl.c:create_snapshot() we jump to the fail label, and after
that we free again the same anonymous device number, which in the
meanwhile may have been reallocated somewhere else, because
pending_snapshot->anon_dev still has the same value as in step 1.
Recently syzbot ran into this and reported the following trace:
------------[ cut here ]------------
ida_free called for id=51 which is not allocated.
WARNING: CPU: 1 PID: 31038 at lib/idr.c:525 ida_free+0x370/0x420 lib/idr.c:525
Modules linked in:
CPU: 1 PID: 31038 Comm: syz-executor.2 Not tainted 6.8.0-rc4-syzkaller-00410-gc02197fc9076 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
RIP: 0010:ida_free+0x370/0x420 lib/idr.c:525
Code: 10 42 80 3c 28 (...)
RSP: 0018:ffffc90015a67300 EFLAGS: 00010246
RAX: be5130472f5dd000 RBX: 0000000000000033 RCX: 0000000000040000
RDX: ffffc90009a7a000 RSI: 000000000003ffff RDI: 0000000000040000
RBP: ffffc90015a673f0 R08: ffffffff81577992 R09: 1ffff92002b4cdb4
R10: dffffc0000000000 R11: fffff52002b4cdb5 R12: 0000000000000246
R13: dffffc0000000000 R14: ffffffff8e256b80 R15: 0000000000000246
FS: 00007fca3f4b46c0(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f167a17b978 CR3: 000000001ed26000 CR4: 0000000000350ef0
Call Trace: