tree e07a78d2e184b152b8cbd85c2928002554ccc33f
parent 38d26d89b31d0766d431471572cc9b007ca19c98
author Daniel Borkmann <daniel@iogearbox.net> 1619186395 +0000
committer Daniel Borkmann <daniel@iogearbox.net> 1619536429 +0200

bpf: Fix propagation of 32 bit unsigned bounds from 64 bit bounds

Similarly as b02709587ea3 ("bpf: Fix propagation of 32-bit signed bounds
from 64-bit bounds."), we also need to fix the propagation of 32 bit
unsigned bounds from 64 bit counterparts. That is, really only set the
u32_{min,max}_value when /both/ {umin,umax}_value safely fit in 32 bit
space. For example, the register with a umin_value == 1 does /not/ imply
that u32_min_value is also equal to 1, since umax_value could be much
larger than 32 bit subregister can hold, and thus u32_min_value is in
the interval [0,1] instead.

Before fix, invalid tracking result of R2_w=inv1:

  [...]
  5: R0_w=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv(id=0) R10=fp0
  5: (35) if r2 >= 0x1 goto pc+1
  [...] // goto path
  7: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,umin_value=1) R10=fp0
  7: (b6) if w2 <= 0x1 goto pc+1
  [...] // goto path
  9: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,smin_value=-9223372036854775807,smax_value=9223372032559808513,umin_value=1,umax_value=18446744069414584321,var_off=(0x1; 0xffffffff00000000),s32_min_value=1,s32_max_value=1,u32_max_value=1) R10=fp0
  9: (bc) w2 = w2
  10: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv1 R10=fp0
  [...]

After fix, correct tracking result of R2_w=inv(id=0,umax_value=1,var_off=(0x0; 0x1)):

  [...]
  5: R0_w=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv(id=0) R10=fp0
  5: (35) if r2 >= 0x1 goto pc+1
  [...] // goto path
  7: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,umin_value=1) R10=fp0
  7: (b6) if w2 <= 0x1 goto pc+1
  [...] // goto path
  9: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,smax_value=9223372032559808513,umax_value=18446744069414584321,var_off=(0x0; 0xffffffff00000001),s32_min_value=0,s32_max_value=1,u32_max_value=1) R10=fp0
  9: (bc) w2 = w2
  10: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv(id=0,umax_value=1,var_off=(0x0; 0x1)) R10=fp0
  [...]

Thus, same issue as in b02709587ea3 holds for unsigned subregister tracking.
Also, align __reg64_bound_u32() similarly to __reg64_bound_s32() as done in
b02709587ea3 to make them uniform again.

Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Reported-by: Manfred Paul (@_manfp)
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>