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19 lines
3.0 KiB
Markdown
19 lines
3.0 KiB
Markdown
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### [CVE-2024-49868](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-49868)
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### Description
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In the Linux kernel, the following vulnerability has been resolved:btrfs: fix a NULL pointer dereference when failed to start a new trasacntion[BUG]Syzbot reported a NULL pointer dereference with the following crash: FAULT_INJECTION: forcing a failure. start_transaction+0x830/0x1670 fs/btrfs/transaction.c:676 prepare_to_relocate+0x31f/0x4c0 fs/btrfs/relocation.c:3642 relocate_block_group+0x169/0xd20 fs/btrfs/relocation.c:3678 ... BTRFS info (device loop0): balance: ended with status: -12 Oops: general protection fault, probably for non-canonical address 0xdffffc00000000cc: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000660-0x0000000000000667] RIP: 0010:btrfs_update_reloc_root+0x362/0xa80 fs/btrfs/relocation.c:926 Call Trace: <TASK> commit_fs_roots+0x2ee/0x720 fs/btrfs/transaction.c:1496 btrfs_commit_transaction+0xfaf/0x3740 fs/btrfs/transaction.c:2430 del_balance_item fs/btrfs/volumes.c:3678 [inline] reset_balance_state+0x25e/0x3c0 fs/btrfs/volumes.c:3742 btrfs_balance+0xead/0x10c0 fs/btrfs/volumes.c:4574 btrfs_ioctl_balance+0x493/0x7c0 fs/btrfs/ioctl.c:3673 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f[CAUSE]The allocation failure happens at the start_transaction() insideprepare_to_relocate(), and during the error handling we callunset_reloc_control(), which makes fs_info->balance_ctl to be NULL.Then we continue the error path cleanup in btrfs_balance() by callingreset_balance_state() which will call del_balance_item() to fully deletethe balance item in the root tree.However during the small window between set_reloc_contrl() andunset_reloc_control(), we can have a subvolume tree update and created areloc_root for that subvolume.Then we go into the final btrfs_commit_transaction() ofdel_balance_item(), and into btrfs_update_reloc_root() insidecommit_fs_roots().That function checks if fs_info->reloc_ctl is in the merge_reloc_treestage, but since fs_info->reloc_ctl is NULL, it results a NULL pointerdereference.[FIX]Just add extra check on fs_info->reloc_ctl insidebtrfs_update_reloc_root(), before checkingfs_info->reloc_ctl->merge_reloc_tree.That DEAD_RELOC_TREE handling is to prevent further modification to thereloc tree during merge stage, but since there is no reloc_ctl at all,we do not need to bother that.
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### POC
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#### Reference
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No PoCs from references.
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#### Github
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- https://github.com/w4zu/Debian_security
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