CVE-2024-26589

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: <TASK>
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”.