CVE-2023-52772 in Linux
Zusammenfassung
von VulDB • 05.06.2026
Implied Question: What is the bug described in this KASAN report?
The bug is a **Use-After-Free (UAF)** vulnerability in the Unix domain socket implementation (`net/unix/af_unix.c`).
### Analysis
1. **The Free Event:** The stack trace under "Freed by task 5295" shows that an `sk_buff` (socket buffer) was freed via `kfree_skbmem` -> `consume_skb`. This happened inside the function `queue_oob` at line **2178** of `net/unix/af_unix.c`.
2. **The Allocation Event:** The stack trace under "Allocated by task 5295" shows that a *new* `sk_buff` was allocated via `alloc_skb` -> `__alloc_skb`. This happened inside the function `queue_oob` at line **2147** of `net/unix/af_unix.c`.
3. **The Conflict:** Both the allocation and the free occur within the same function `queue_oob` in the same task. This indicates that the code is attempting to use or access a buffer that was just freed, or more likely, there is a logic error where a buffer is freed prematurely while still being referenced or processed, or the allocation is happening after a free in a way that suggests a race or incorrect state management.
However, looking closely at the line numbers: * Free at line 2178 * Alloc at line 2147
This sequence (Free then Alloc) in the same function call stack for the same task is unusual for a simple UAF unless the "Allocated by task" stack is from a *different* invocation or the "Freed by task" stack is from a *different* invocation. But KASAN reports typically show the *current* access (which triggered the fault) and the *previous* free.
Let's re-read the standard KASAN output format: * **Allocated by task:** This is the stack trace where the memory was *originally allocated*. * **Freed by task:** This is the stack trace where the memory was *freed*. * **The Bug:** The current access (not shown in the truncated part, but implied by the report) is accessing memory that was freed in the "Freed by task" trace, but was allocated in the "Allocated by task" trace.
Wait, the "Allocated by task" trace ends with `queue_oob` at line 2147. The "Freed by task" trace ends with `queue_oob` at line 2178.
This implies: 1. A buffer was allocated in `queue_oob` (line 2147). 2. That same buffer was later freed in `queue_oob` (line 2178). 3. The bug is that the buffer is being accessed *after* it was freed at line 2178.
The truncated part likely shows the current access that triggered the KASAN error. The access is happening after the free at line 2178.
**Root Cause:** In `queue_oob`, an `sk_buff` is allocated (line 2147). Later in the same function, it is freed (line 2178). However, the code continues to use or access this buffer after the free, or there is a path where the buffer is freed but still referenced.
Looking at the Linux kernel source for `net/unix/af_unix.c` (around version 5.10+), the `queue_oob` function handles out-of-band data. The issue is likely that the `sk_buff` allocated for the OOB data is freed, but a pointer to it is stored in a control message or passed along, leading to a use-after-free when that control message is processed later.
Specifically, in older versions of the kernel, there was a bug where the `sk_buff` containing the OOB data was freed, but the `scm` (socket control message) structure still held a reference or the data was copied in a way that relied on the buffer's lifetime.
**Conclusion:** The bug is a **Use-After-Free** in `net/unix/af_unix.c` in the `queue_oob` function. An `sk_buff` is allocated, then freed, but subsequently accessed.
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