diff mbox series

[SRU,F,1/1] bpf: Reject variable offset alu on PTR_TO_FLOW_KEYS

Message ID 20240314194617.42266-3-bethany.jamison@canonical.com
State New
Headers show
Series [SRU,F,1/1] bpf: Reject variable offset alu on PTR_TO_FLOW_KEYS | expand

Commit Message

Bethany Jamison March 14, 2024, 7:46 p.m. UTC 
From: Hao Sun <sunhao.th@gmail.com>

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".

Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook")
Signed-off-by: Hao Sun <sunhao.th@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240115082028.9992-1-sunhao.th@gmail.com
(backported from commit 22c7fa171a02d310e3a3f6ed46a698ca8a0060ed)
[bjamison: upstream moved a case in 'switch (ptr_reg->type)' to an if-block
before the switch block, this creates a context conflict for Focal when
applying the fix commit but is logically the same, I kept the conflicting case
in the switch block and added the fix commit changes as given]
CVE-2024-26589
Signed-off-by: Bethany Jamison <bethany.jamison@canonical.com>
---
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e132c18f03e23..5a375e28bfeaf 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4664,6 +4664,10 @@  static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 		verbose(env, "R%d pointer arithmetic on %s prohibited, null-check it first\n",
 			dst, reg_type_str[ptr_reg->type]);
 		return -EACCES;
+	case PTR_TO_FLOW_KEYS:
+		if (known)
+			break;
+		fallthrough;
 	case CONST_PTR_TO_MAP:
 		/* smin_val represents the known value */
 		if (known && smin_val == 0 && opcode == BPF_ADD)