CVE-2024-53680 ipvs: fix UB due to uninitialized stack access in ip_vs_protocol_init()
Uninitialized stack access in Linux kernel IPVS module causes oops or boot panic, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-53680?
CVE-2024-53680 is a medium-severity vulnerability in Linux kernel, published on 11 Jan 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ipvs: fix UB due to uninitialized stack access in ip_vs_protocol_init()
Under certain kernel configurations when building with Clang/LLVM, the compiler does not generate a return or jump as the terminator instruction for ip_vs_protocol_init(), triggering the following objtool warning during build time:
vmlinux.o: warning: objtool: ip_vs_protocol_init() falls through to next function __initstub__kmod_ip_vs_rr__935_123_ip_vs_rr_init6()
At runtime, this either causes an oops when trying to load the ipvs module or a boot-time panic if ipvs is built-in. This same issue has been reported by the Intel kernel test robot previously.
Digging deeper into both LLVM and the kernel code reveals this to be a undefined behavior problem. ip_vs_protocol_init() uses a on-stack buffer of 64 chars to store the registered protocol names and leaves it uninitialized after definition. The function calls strnlen() when concatenating protocol names into the buffer. With CONFIG_FORTIFY_SOURCE strnlen() performs an extra step to check whether the last byte of the input char buffer is a null character (commit 3009f891bb9f ("fortify: Allow strlen() and strnlen() to pass compile-time known lengths")). This, together with possibly other configurations, cause the following IR to be generated:
define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #5 section ".init.text" align 16 !kcfi_type !29 { %1 = alloca [64 x i8], align 16 ...
14: ; preds = %11 %15 = getelementptr inbounds i8, ptr %1, i64 63 %16 = load i8, ptr %15, align 1 %17 = tail call i1 @llvm.is.constant.i8(i8 %16) %18 = icmp eq i8 %16, 0 %19 = select i1 %17, i1 %18, i1 false br i1 %19, label %20, label %23
20: ; preds = %14 %21 = call i64 @strlen(ptr noundef nonnull dereferenceable(1) %1) #23 ...
23: ; preds = %14, %11, %20 %24 = call i64 @strnlen(ptr noundef nonnull dereferenceable(1) %1, i64 noundef 64) #24 ... }
The above code calculates the address of the last char in the buffer (value %15) and then loads from it (value %16). Because the buffer is never initialized, the LLVM GVN pass marks value %16 as undefined:
%13 = getelementptr inbounds i8, ptr %1, i64 63 br i1 undef, label %14, label %17
This gives later passes (SCCP, in particular) more DCE opportunities by propagating the undef value further, and eventually removes everything after the load on the uninitialized stack location:
define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #0 section ".init.text" align 16 !kcfi_type !11 { %1 = alloca [64 x i8], align 16 ...
12: ; preds = %11 %13 = getelementptr inbounds i8, ptr %1, i64 63 unreachable }
In this way, the generated native code will just fall through to the next function, as LLVM does not generate any code for the unreachable IR instruction and leaves the function without a terminator.
Zero the on-stack buffer to avoid this possible UB.
Weakness: CWE-908
Which versions are affected by CVE-2024-53680?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-53680?
Apply the vendor's patch.
Is CVE-2024-53680 being exploited?
There is no known exploitation of CVE-2024-53680 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-53680, DEBIAN-CVE-2024-53680, GHSA-5f32-qq4v-9hch, UBUNTU-CVE-2024-53680.