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

ipc: limit next_id allocation to the valid ID range

The checkpoint/restore sysctl path can request the next SysV IPC id
through ids->next_id.  ipc_idr_alloc() currently forwards that request to
idr_alloc() with an open-ended upper bound.

If the valid tail of the SysV IPC id space is full, the allocation can
spill beyond ipc_mni.  The returned SysV IPC id still uses the normal
index encoding, so later lookup and removal can target the wrong slot. 
This leaves the real IDR entry behind and breaks the IDR state for the
object.

The bug is in ipc_idr_alloc() in the checkpoint/restore path.

1. ids->next_id is passed to:

       idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id), 0, ...)

2. The zero upper bound makes the allocation effectively open-ended.
   Once the valid SysV IPC tail is occupied, idr_alloc() can spill past
   ipc_mni and allocate an entry beyond the valid IPC id range.

3. The new object id is still encoded with the narrower SysV IPC index
   width:

       new->id = (new->seq << ipcmni_seq_shift()) + idx

4. Later removal goes through ipc_rmid(), which uses:

       ipcid_to_idx(ipcp->id)

   That truncates the real IDR index. An object actually stored at a
   high index can then be removed as if it lived at a low in-range
   index.

5. For shared memory, shm_destroy() frees the current object anyway, but
   the real high IDR slot is left behind as a dangling pointer.

6. A subsequent walk of /proc/sysvipc/shm reaches the stale IDR entry
   and dereferences freed memory.

Prevent this by bounding the requested allocation to ipc_mni so the
checkpoint/restore path fails once the valid range is exhausted.

https://git.kernel.org/stable/c/157ce2c6836ce0ff19108a819f38df061345425f

https://git.kernel.org/stable/c/3bbe2bb9111ce6967a951bfac79af142d816fae5

https://git.kernel.org/stable/c/41058d4c3f63ab64901560a704882e0565f4e456

https://git.kernel.org/stable/c/8c58a92849175f5e2ab7bc2734b3b89afe79f6ef

https://git.kernel.org/stable/c/a3cc795129e5ec0f8948653a3bf471e7d8852f5e

https://git.kernel.org/stable/c/af24e202b543ded8a34f1d5d3db54eb916173f04

https://git.kernel.org/stable/c/bd4be70669af55b974860d13680348cfdf50bbed

https://git.kernel.org/stable/c/fa0b9b2b7ae3539908d69c2b9ac0d144d9bc5139

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