CVE-2024-26853

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

igc: avoid returning frame twice in XDP_REDIRECT

When a frame can not be transmitted in XDP_REDIRECT (e.g. due to a full queue), it is necessary to free it by calling xdp_return_frame_rx_napi.

However, this is the responsibility of the caller of the ndo_xdp_xmit (see for example bq_xmit_all in kernel/bpf/devmap.c) and thus calling it inside igc_xdp_xmit (which is the ndo_xdp_xmit of the igc driver) as well will lead to memory corruption.

In fact, bq_xmit_all expects that it can return all frames after the last successfully transmitted one. Therefore, break for the first not transmitted frame, but do not call xdp_return_frame_rx_napi in igc_xdp_xmit. This is equally implemented in other Intel drivers such as the igb.

There are two alternatives to this that were rejected:

1. Return num_frames as all the frames would have been transmitted and release them inside igc_xdp_xmit. While it might work technically, it is not what the return value is meant to represent (i.e. the number of SUCCESSFULLY transmitted packets).
2. Rework kernel/bpf/devmap.c and all drivers to support non-consecutively dropped packets. Besides being complex, it likely has a negative performance impact without a significant gain since it is anyway unlikely that the next frame can be transmitted if the previous one was dropped.

The memory corruption can be reproduced with the following script which leads to a kernel panic after a few seconds. It basically generates more traffic than a i225 NIC can transmit and pushes it via XDP_REDIRECT from a virtual interface to the physical interface where frames get dropped.

#!/bin/bash INTERFACE=enp4s0 INTERFACE_IDX=cat /sys/class/net/$INTERFACE/ifindex

sudo ip link add dev veth1 type veth peer name veth2 sudo ip link set up $INTERFACE sudo ip link set up veth1 sudo ip link set up veth2

cat « EOF > redirect.bpf.c

SEC(prog) int redirect(struct xdp_md *ctx) { return bpf_redirect($INTERFACE_IDX, 0); }

char _license[] SEC(license) = GPL; EOF clang -O2 -g -Wall -target bpf -c redirect.bpf.c -o redirect.bpf.o sudo ip link set veth2 xdp obj redirect.bpf.o

cat « EOF > pass.bpf.c

SEC(prog) int pass(struct xdp_md *ctx) { return XDP_PASS; }

char _license[] SEC(license) = GPL; EOF clang -O2 -g -Wall -target bpf -c pass.bpf.c -o pass.bpf.o sudo ip link set $INTERFACE xdp obj pass.bpf.o

cat « EOF > trafgen.cfg

{ /* Ethernet Header */ 0xe8, 0x6a, 0x64, 0x41, 0xbf, 0x46, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, const16(ETH_P_IP),

 /* IPv4 Header */
 0b01000101, 0,   # IPv4 version, IHL, TOS
 const16(1028),   # IPv4 total length (UDP length + 20 bytes (IP header))
 const16(2),      # IPv4 ident
 0b01000000, 0,   # IPv4 flags, fragmentation off
 64,              # IPv4 TTL
 17,              # Protocol UDP
 csumip(14, 33),  # IPv4 checksum

 /* UDP Header */
 10,  0, 1, 1,    # IP Src - adapt as needed
 10,  0, 1, 2,    # IP Dest - adapt as needed
 const16(6666),   # UDP Src Port
 const16(6666),   # UDP Dest Port
 const16(1008),   # UDP length (UDP header 8 bytes + payload length)
 csumudp(14, 34), # UDP checksum

 /* Payload */
 fill(W, 1000),

} EOF

sudo trafgen -i trafgen.cfg -b3000MB -o veth1 –cpp

Weakness

The product writes data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

• Be wary that a language’s interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

• Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

• D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

• Consider adhering to the following rules when allocating and managing an application’s memory:

• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

• Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

• For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

References

• https://git.kernel.org/stable/c/1b3b8231386a572bac8cd5b6fd7e944b84f9bb1f
• https://git.kernel.org/stable/c/63a3c1f3c9ecc654d851e7906d05334cd0c236e2
• https://git.kernel.org/stable/c/8df393af9e7e8dfd62e9c41dbaa4d2ff53bf794a
• https://git.kernel.org/stable/c/ef27f655b438bed4c83680e4f01e1cde2739854b
• https://git.kernel.org/stable/c/1b3b8231386a572bac8cd5b6fd7e944b84f9bb1f
• https://git.kernel.org/stable/c/63a3c1f3c9ecc654d851e7906d05334cd0c236e2
• https://git.kernel.org/stable/c/8df393af9e7e8dfd62e9c41dbaa4d2ff53bf794a
• https://git.kernel.org/stable/c/ef27f655b438bed4c83680e4f01e1cde2739854b