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linux/kernel/bpf
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Daniel Borkmann 3844d153a4 bpf: Fix insufficient bounds propagation from adjust_scalar_min_max_vals 
Kuee reported a corner case where the tnum becomes constant after the call
to __reg_bound_offset(), but the register's bounds are not, that is, its
min bounds are still not equal to the register's max bounds.

This in turn allows to leak pointers through turning a pointer register as
is into an unknown scalar via adjust_ptr_min_max_vals().

Before:

  func#0 @0
  0: R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0))
  0: (b7) r0 = 1                        ; R0_w=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0))
  1: (b7) r3 = 0                        ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0))
  2: (87) r3 = -r3                      ; R3_w=scalar()
  3: (87) r3 = -r3                      ; R3_w=scalar()
  4: (47) r3 |= 32767                   ; R3_w=scalar(smin=-9223372036854743041,umin=32767,var_off=(0x7fff; 0xffffffffffff8000),s32_min=-2147450881)
  5: (75) if r3 s>= 0x0 goto pc+1       ; R3_w=scalar(umin=9223372036854808575,var_off=(0x8000000000007fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767)
  6: (95) exit

  from 5 to 7: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0))
  7: (d5) if r3 s<= 0x8000 goto pc+1    ; R3=scalar(umin=32769,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767)
  8: (95) exit

  from 7 to 9: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0))
  9: (07) r3 += -32767                  ; R3_w=scalar(imm=0,umax=1,var_off=(0x0; 0x0))  <--- [*]
  10: (95) exit

What can be seen here is that R3=scalar(umin=32767,umax=32768,var_off=(0x7fff;
0x8000)) after the operation R3 += -32767 results in a 'malformed' constant, that
is, R3_w=scalar(imm=0,umax=1,var_off=(0x0; 0x0)). Intersecting with var_off has
not been done at that point via __update_reg_bounds(), which would have improved
the umax to be equal to umin.

Refactor the tnum <> min/max bounds information flow into a reg_bounds_sync()
helper and use it consistently everywhere. After the fix, bounds have been
corrected to R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) and thus the register
is regarded as a 'proper' constant scalar of 0.

After:

  func#0 @0
  0: R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0))
  0: (b7) r0 = 1                        ; R0_w=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0))
  1: (b7) r3 = 0                        ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0))
  2: (87) r3 = -r3                      ; R3_w=scalar()
  3: (87) r3 = -r3                      ; R3_w=scalar()
  4: (47) r3 |= 32767                   ; R3_w=scalar(smin=-9223372036854743041,umin=32767,var_off=(0x7fff; 0xffffffffffff8000),s32_min=-2147450881)
  5: (75) if r3 s>= 0x0 goto pc+1       ; R3_w=scalar(umin=9223372036854808575,var_off=(0x8000000000007fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767)
  6: (95) exit

  from 5 to 7: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0))
  7: (d5) if r3 s<= 0x8000 goto pc+1    ; R3=scalar(umin=32769,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767)
  8: (95) exit

  from 7 to 9: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0))
  9: (07) r3 += -32767                  ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0))  <--- [*]
  10: (95) exit

Fixes: b03c9f9fdc ("bpf/verifier: track signed and unsigned min/max values")
Reported-by: Kuee K1r0a <liulin063@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20220701124727.11153-2-daniel@iogearbox.net
2022-07-01 12:56:27 -07:00
..
preload bpf: Remove redundant slash 2022-03-07 22:19:32 -08:00
arraymap.c bpf: add bpf_map_lookup_percpu_elem for percpu map 2022-05-11 18:16:54 -07:00
bloom_filter.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
bpf_inode_storage.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
bpf_iter.c bpf: Remove redundant assignment to meta.seq in __task_seq_show() 2022-04-11 21:14:34 +02:00
bpf_local_storage.c bpf: Fix usage of trace RCU in local storage. 2022-04-19 17:55:45 -07:00
bpf_lru_list.c bpf_lru_list: Read double-checked variable once without lock 2021-02-10 15:54:26 -08:00
bpf_lru_list.h printk: stop including cache.h from printk.h 2022-05-13 07:20:07 -07:00
bpf_lsm.c bpf, x86: Attach a cookie to fentry/fexit/fmod_ret/lsm. 2022-05-10 21:58:31 -07:00
bpf_struct_ops_types.h bpf: Add dummy BPF STRUCT_OPS for test purpose 2021-11-01 14:10:00 -07:00
bpf_struct_ops.c bpf, x86: Generate trampolines from bpf_tramp_links 2022-05-10 17:50:40 -07:00
bpf_task_storage.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
btf.c bpf: Limit maximum modifier chain length in btf_check_type_tags 2022-06-15 19:32:12 +02:00
cgroup.c bpf: Use bpf_prog_run_array_cg_flags everywhere 2022-04-25 17:03:57 -07:00
core.c bpf: Fix probe read error in ___bpf_prog_run() 2022-05-28 01:09:18 +02:00
cpumap.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
devmap.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
disasm.c bpf: Relicense disassembler as GPL-2.0-only OR BSD-2-Clause 2021-09-02 14:49:23 +02:00
disasm.h bpf: Relicense disassembler as GPL-2.0-only OR BSD-2-Clause 2021-09-02 14:49:23 +02:00
dispatcher.c
hashtab.c bpf: add bpf_map_lookup_percpu_elem for percpu map 2022-05-11 18:16:54 -07:00
helpers.c bpf: Add dynptr data slices 2022-05-23 14:31:28 -07:00
inode.c bpf: Convert bpf_preload.ko to use light skeleton. 2022-02-10 23:31:51 +01:00
Kconfig rcu: Make the TASKS_RCU Kconfig option be selected 2022-04-20 16:52:58 -07:00
link_iter.c bpf: Add bpf_link iterator 2022-05-10 11:20:45 -07:00
local_storage.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
lpm_trie.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
Makefile bpf: Add bpf_link iterator 2022-05-10 11:20:45 -07:00
map_in_map.c bpf: Allow storing unreferenced kptr in map 2022-04-25 17:31:35 -07:00
map_in_map.h bpf: Add map_meta_equal map ops 2020-08-28 15:41:30 +02:00
map_iter.c bpf: Introduce MEM_RDONLY flag 2021-12-18 13:27:41 -08:00
mmap_unlock_work.h bpf: Introduce helper bpf_find_vma 2021-11-07 11:54:51 -08:00
net_namespace.c net: Add includes masked by netdevice.h including uapi/bpf.h 2021-12-29 20:03:05 -08:00
offload.c
percpu_freelist.c bpf: Use raw_spin_trylock() for pcpu_freelist_push/pop in NMI 2020-10-06 00:04:11 +02:00
percpu_freelist.h bpf: Use raw_spin_trylock() for pcpu_freelist_push/pop in NMI 2020-10-06 00:04:11 +02:00
prog_iter.c bpf: Refactor bpf_iter_reg to have separate seq_info member 2020-07-25 20:16:32 -07:00
queue_stack_maps.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
reuseport_array.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
ringbuf.c bpf: Dynptr support for ring buffers 2022-05-23 14:31:28 -07:00
stackmap.c bpf: Compute map_btf_id during build time 2022-04-26 11:35:21 -07:00
syscall.c bpf: refine kernel.unprivileged_bpf_disabled behaviour 2022-05-20 19:48:29 -07:00
sysfs_btf.c bpf: Load and verify kernel module BTFs 2020-11-10 15:25:53 -08:00
task_iter.c bpf: Remove redundant assignment to meta.seq in __task_seq_show() 2022-04-11 21:14:34 +02:00
tnum.c bpf, tnums: Provably sound, faster, and more precise algorithm for tnum_mul 2021-06-01 13:34:15 +02:00
trampoline.c bpf: Fix potential array overflow in bpf_trampoline_get_progs() 2022-05-11 21:24:20 -07:00
verifier.c bpf: Fix insufficient bounds propagation from adjust_scalar_min_max_vals 2022-07-01 12:56:27 -07:00