CVE-2023-53790

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

bpf: Zeroing allocated object from slab in bpf memory allocator

Currently the freed element in bpf memory allocator may be immediately reused, for htab map the reuse will reinitialize special fields in map value (e.g., bpf_spin_lock), but lookup procedure may still access these special fields, and it may lead to hard-lockup as shown below:

NMI backtrace for cpu 16 CPU: 16 PID: 2574 Comm: htab.bin Tainted: G L 6.1.0+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), RIP: 0010:queued_spin_lock_slowpath+0x283/0x2c0 ...... Call Trace: <TASK> copy_map_value_locked+0xb7/0x170 bpf_map_copy_value+0x113/0x3c0 __sys_bpf+0x1c67/0x2780 __x64_sys_bpf+0x1c/0x20 do_syscall_64+0x30/0x60 entry_SYSCALL_64_after_hwframe+0x46/0xb0 ...... </TASK>

For htab map, just like the preallocated case, these is no need to initialize these special fields in map value again once these fields have been initialized. For preallocated htab map, these fields are initialized through __GFP_ZERO in bpf_map_area_alloc(), so do the similar thing for non-preallocated htab in bpf memory allocator. And there is no need to use __GFP_ZERO for per-cpu bpf memory allocator, because __alloc_percpu_gfp() does it implicitly.

A flaw in the Linux kernel's BPF memory allocator affects Red Hat Enterprise Linux 9 with low impact. When an element freed by the BPF memory allocator is immediately reused for a non-preallocated hash (htab) map, special fields in the map value (for example bpf_spin_lock) are reinitialized while a concurrent lookup may still be accessing those fields. A local user with privileges to perform BPF map operations (typically CAP_BPF or CAP_SYS_ADMIN) could exploit this race to cause a kernel hard lockup, resulting in a denial of service of the affected system; confidentiality and integrity are not impacted. Within Red Hat Enterprise Linux 9, the kernel and kernel-rt packages in the 9.0 and 9.2 z-stream update streams are affected; the fix is deferred for these streams due to the flaw's low severity, and the residual risk is that a local privileged user could trigger a system hang (denial of service). The other Red Hat Enterprise Linux streams and versions, Red Hat Enterprise Linux 10, and Red Hat In-Vehicle OS are not affected because the vulnerable code is not present in their kernels. Red Hat rates this flaw Low (CVSS 5.5) while the CVE.org record scores it 7.8 (Important); the difference reflects that exploitation requires local access with BPF privileges and the demonstrated consequence is limited to availability.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.