Description

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

bpf: Reject variable offset alu on PTR_TO_FLOW_KEYS

For PTR_TO_FLOW_KEYS, check_flow_keys_access() only uses fixed off
for validation. However, variable offset ptr alu is not prohibited
for this ptr kind. So the variable offset is not checked.

The following prog is accepted:

func#0 @0
0: R1=ctx() R10=fp0
0: (bf) r6 = r1 ; R1=ctx() R6_w=ctx()
1: (79) r7 = *(u64 *)(r6 +144) ; R6_w=ctx() R7_w=flow_keys()
2: (b7) r8 = 1024 ; R8_w=1024
3: (37) r8 /= 1 ; R8_w=scalar()
4: (57) r8 &= 1024 ; R8_w=scalar(smin=smin32=0,
smax=umax=smax32=umax32=1024,var_off=(0x0; 0x400))
5: (0f) r7 += r8
mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1
mark_precise: frame0: regs=r8 stack= before 4: (57) r8 &= 1024
mark_precise: frame0: regs=r8 stack= before 3: (37) r8 /= 1
mark_precise: frame0: regs=r8 stack= before 2: (b7) r8 = 1024
6: R7_w=flow_keys(smin=smin32=0,smax=umax=smax32=umax32=1024,var_off
=(0x0; 0x400)) R8_w=scalar(smin=smin32=0,smax=umax=smax32=umax32=1024,
var_off=(0x0; 0x400))
6: (79) r0 = *(u64 *)(r7 +0) ; R0_w=scalar()
7: (95) exit

This prog loads flow_keys to r7, and adds the variable offset r8
to r7, and finally causes out-of-bounds access:

BUG: unable to handle page fault for address: ffffc90014c80038
[...]
Call Trace:

bpf_dispatcher_nop_func include/li...

Classification

CVE ID: CVE-2024-26589

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 5.08% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/29ffa63f21bcdcef3e36b03cccf9d0cd031f6ab0
https://git.kernel.org/stable/c/4108b86e324da42f7ed425bd71632fd844300dc8
https://git.kernel.org/stable/c/e8d3872b617c21100c5ee4f64e513997a68c2e3d
https://git.kernel.org/stable/c/1b500d5d6cecf98dd6ca88bc9e7ae1783c83e6d3
https://git.kernel.org/stable/c/22c7fa171a02d310e3a3f6ed46a698ca8a0060ed

Timeline