# CVE-2021-47089: linux: In the Linux kernel, the following vulnerability has been resolved:  kfence: fix memory leak when cat kfence objects...

CVE-2021-47089 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47089, released March 4, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47089
- Priority: Routine
- CVSS: 3.3 (low)
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 4, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  kfence: fix memory leak when cat kfence objects  Hulk robot reported a kmemleak problem:      unreferenced object 0xffff93d1d8cc02e8 (size 248):       comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s)       hex dump (first 32 bytes):         00 40 85 19 d4 93 ff ff 00 10 00 00 00 00 00 00  .@..............         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................       backtrace:          seq_open+0x2a/0x80          full_proxy_open+0x167/0x1e0          do_dentry_open+0x1e1/0x3a0          path_openat+0x961/0xa20          do_filp_open+0xae/0x120          do_sys_openat2+0x216/0x2f0          do_sys_open+0x57/0x80          do_syscall_64+0x33/0x40          entry_SYSCALL_64_after_hwframe+0x44/0xa9     unreferenced object 0xffff93d419854000 (size 4096):       comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s)       hex dump (first 32 bytes):         6b 66 65 6e 63 65 2d 23 32 35 30 3a 20 30 78 30  kfence-#250: 0x0         30 30 30 30 30 30 30 37 35 34 62 64 61 31 32 2d  0000000754bda12-       backtrace:          seq_read_iter+0x313/0x440          seq_read+0x14b/0x1a0          full_proxy_read+0x56/0x80          vfs_read+0xa5/0x1b0          ksys_read+0xa0/0xf0          do_syscall_64+0x33/0x40          entry_SYSCALL_64_after_hwframe+0x44/0xa9  I find that we can easily reproduce this problem with the following commands:  	cat /sys/kernel/debug/kfence/objects 	echo scan > /sys/kernel/debug/kmemleak 	cat /sys/kernel/debug/kmemleak  The leaked memory is allocated in the stack below:      do_syscall_64       do_sys_open         do_dentry_open           full_proxy_open             seq_open            ---> alloc seq_file       vfs_read         full_proxy_read           seq_read             seq_read_iter               traverse          ---> alloc seq_buf  And it should have been released in the following process:      do_syscall_64       syscall_exit_to_user_mode         exit_to_user_mode_prepare           task_work_run             ____fput               __fput                 full_proxy_release  ---> free here  However, the release function corresponding to file_operations is not implemented in kfence.  As a result, a memory leak occurs.  Therefore, the solution to this problem is to implement the corresponding release function.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.15-1 | [DEBIAN-CVE-2021-47089](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47089.md) | Mar 4, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.15-1 | [DEBIAN-CVE-2021-47089](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47089.md) | Mar 4, 2024 |
| Linux | linux Debian 14 | 5.15.15-1 | [DEBIAN-CVE-2021-47089](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47089.md) | Mar 4, 2024 |

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