CVE-2024-26589 Information

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:

func0 @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=1024var_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=0smax=umax=smax32=umax32=1024var_off =(0x0; 0x400)) R8_w=scalar(smin=smin32=0smax=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/linux/bpf.h:1231 [inline] __bpf_prog_run include/linux/filter.h:651 [inline] bpf_prog_run include/linux/filter.h:658 [inline] bpf_prog_run_pin_on_cpu include/linux/filter.h:675 [inline] bpf_flow_dissect+0x15f/0x350 net/core/flow_dissector.c:991 bpf_prog_test_run_flow_dissector+0x39d/0x620 net/bpf/test_run.c:1359 bpf_prog_test_run kernel/bpf/syscall.c:4107 [inline] __sys_bpf+0xf8f/0x4560 kernel/bpf/syscall.c:5475 __do_sys_bpf kernel/bpf/syscall.c:5561 [inline] __se_sys_bpf kernel/bpf/syscall.c:5559 [inline] __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:5559 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x3f/0x110 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Fix this by rejecting ptr alu with variable offset on flow_keys. Applying the patch rejects the program with \R7 pointer arithmetic on flow_keys prohibited.

Reference

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