[PATCH AUTOSEL 6.10 15/27] bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses

From: Sasha Levin
Date: Sat Jul 27 2024 - 21:11:14 EST

From: Matt Bobrowski <mattbobrowski@xxxxxxxxxx>

[ Upstream commit ec2b9a5e11e51fea1bb04c1e7e471952e887e874 ]

Currently, it's possible to pass in a modified CONST_PTR_TO_DYNPTR to
a global function as an argument. The adverse effects of this is that
BPF helpers can continue to make use of this modified
CONST_PTR_TO_DYNPTR from within the context of the global function,
which can unintentionally result in out-of-bounds memory accesses and
therefore compromise overall system stability i.e.

[ 244.157771] BUG: KASAN: slab-out-of-bounds in bpf_dynptr_data+0x137/0x140
[ 244.161345] Read of size 8 at addr ffff88810914be68 by task test_progs/302
[ 244.167151] CPU: 0 PID: 302 Comm: test_progs Tainted: G O E 6.10.0-rc3-00131-g66b586715063 #533
[ 244.174318] Call Trace:
[ 244.175787] <TASK>
[ 244.177356] dump_stack_lvl+0x66/0xa0
[ 244.179531] print_report+0xce/0x670
[ 244.182314] ? __virt_addr_valid+0x200/0x3e0
[ 244.184908] kasan_report+0xd7/0x110
[ 244.187408] ? bpf_dynptr_data+0x137/0x140
[ 244.189714] ? bpf_dynptr_data+0x137/0x140
[ 244.192020] bpf_dynptr_data+0x137/0x140
[ 244.194264] bpf_prog_b02a02fdd2bdc5fa_global_call_bpf_dynptr_data+0x22/0x26
[ 244.198044] bpf_prog_b0fe7b9d7dc3abde_callback_adjust_bpf_dynptr_reg_off+0x1f/0x23
[ 244.202136] bpf_user_ringbuf_drain+0x2c7/0x570
[ 244.204744] ? 0xffffffffc0009e58
[ 244.206593] ? __pfx_bpf_user_ringbuf_drain+0x10/0x10
[ 244.209795] bpf_prog_33ab33f6a804ba2d_user_ringbuf_callback_const_ptr_to_dynptr_reg_off+0x47/0x4b
[ 244.215922] bpf_trampoline_6442502480+0x43/0xe3
[ 244.218691] __x64_sys_prlimit64+0x9/0xf0
[ 244.220912] do_syscall_64+0xc1/0x1d0
[ 244.223043] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 244.226458] RIP: 0033:0x7ffa3eb8f059
[ 244.228582] Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 8f 1d 0d 00 f7 d8 64 89 01 48
[ 244.241307] RSP: 002b:00007ffa3e9c6eb8 EFLAGS: 00000206 ORIG_RAX: 000000000000012e
[ 244.246474] RAX: ffffffffffffffda RBX: 00007ffa3e9c7cdc RCX: 00007ffa3eb8f059
[ 244.250478] RDX: 00007ffa3eb162b4 RSI: 0000000000000000 RDI: 00007ffa3e9c7fb0
[ 244.255396] RBP: 00007ffa3e9c6ed0 R08: 00007ffa3e9c76c0 R09: 0000000000000000
[ 244.260195] R10: 0000000000000000 R11: 0000000000000206 R12: ffffffffffffff80
[ 244.264201] R13: 000000000000001c R14: 00007ffc5d6b4260 R15: 00007ffa3e1c7000
[ 244.268303] </TASK>

Add a check_func_arg_reg_off() to the path in which the BPF verifier
verifies the arguments of global function arguments, specifically
those which take an argument of type ARG_PTR_TO_DYNPTR |
MEM_RDONLY. Also, process_dynptr_func() doesn't appear to perform any
explicit and strict type matching on the supplied register type, so
let's also enforce that a register either type PTR_TO_STACK or
CONST_PTR_TO_DYNPTR is by the caller.

Reported-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Signed-off-by: Matt Bobrowski <mattbobrowski@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240625062857.92760-1-mattbobrowski@xxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/bpf/verifier.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 214a9fa8c6fb7..87e242f37f46e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7715,6 +7715,13 @@ static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
int err;

+ if (reg->type != PTR_TO_STACK && reg->type != CONST_PTR_TO_DYNPTR) {
+ verbose(env,
+ "arg#%d expected pointer to stack or const struct bpf_dynptr\n",
+ regno);
+ return -EINVAL;
+ }
+
/* MEM_UNINIT and MEM_RDONLY are exclusive, when applied to an
* ARG_PTR_TO_DYNPTR (or ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_*):
*/
@@ -9464,6 +9471,10 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
return -EINVAL;
}
} else if (arg->arg_type == (ARG_PTR_TO_DYNPTR | MEM_RDONLY)) {
+ ret = check_func_arg_reg_off(env, reg, regno, ARG_PTR_TO_DYNPTR);
+ if (ret)
+ return ret;
+
ret = process_dynptr_func(env, regno, -1, arg->arg_type, 0);
if (ret)
return ret;
@@ -11957,12 +11968,6 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
enum bpf_arg_type dynptr_arg_type = ARG_PTR_TO_DYNPTR;
int clone_ref_obj_id = 0;

- if (reg->type != PTR_TO_STACK &&
- reg->type != CONST_PTR_TO_DYNPTR) {
- verbose(env, "arg#%d expected pointer to stack or dynptr_ptr\n", i);
- return -EINVAL;
- }
-
if (reg->type == CONST_PTR_TO_DYNPTR)
dynptr_arg_type |= MEM_RDONLY;

--
2.43.0