# CVE-2021-47615: linux: In the Linux kernel, the following vulnerability has been resolved:  RDMA/mlx5: Fix releasing unallocated memory in d...

CVE-2021-47615 is fixed in linux on 1 platform, first by CVE-2021-47615, released June 19, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47615
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: n/a
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 19, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  RDMA/mlx5: Fix releasing unallocated memory in dereg MR flow  For the case of IB_MR_TYPE_DM the mr does doesn't have a umem, even though it is a user MR. This causes function mlx5_free_priv_descs() to think that it is a kernel MR, leading to wrongly accessing mr->descs that will get wrong values in the union which leads to attempt to release resources that were not allocated in the first place.  For example:  DMA-API: mlx5_core 0000:08:00.1: device driver tries to free DMA memory it has not allocated [device address=0x0000000000000000] [size=0 bytes]  WARNING: CPU: 8 PID: 1021 at kernel/dma/debug.c:961 check_unmap+0x54f/0x8b0  RIP: 0010:check_unmap+0x54f/0x8b0  Call Trace:   debug_dma_unmap_page+0x57/0x60   mlx5_free_priv_descs+0x57/0x70 [mlx5_ib]   mlx5_ib_dereg_mr+0x1fb/0x3d0 [mlx5_ib]   ib_dereg_mr_user+0x60/0x140 [ib_core]   uverbs_destroy_uobject+0x59/0x210 [ib_uverbs]   uobj_destroy+0x3f/0x80 [ib_uverbs]   ib_uverbs_cmd_verbs+0x435/0xd10 [ib_uverbs]   ? uverbs_finalize_object+0x50/0x50 [ib_uverbs]   ? lock_acquire+0xc4/0x2e0   ? lock_acquired+0x12/0x380   ? lock_acquire+0xc4/0x2e0   ? lock_acquire+0xc4/0x2e0   ? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]   ? lock_release+0x28a/0x400   ib_uverbs_ioctl+0xc0/0x140 [ib_uverbs]   ? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]   __x64_sys_ioctl+0x7f/0xb0   do_syscall_64+0x38/0x90  Fix it by reorganizing the dereg flow and mlx5_ib_mr structure:  - Move the ib_umem field into the user MRs structure in the union as it's    applicable only there.  - Function mlx5_ib_dereg_mr() will now call mlx5_free_priv_descs() only    in case there isn't udata, which indicates that this isn't a user MR.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.15-1 | [CVE-2021-47615](https://patchblox.com/security/data/fix/linux/cve-2021-47615.md) | Jun 19, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.15-1 | [CVE-2021-47615](https://patchblox.com/security/data/fix/linux/cve-2021-47615.md) | Jun 19, 2024 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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