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bpf: Fix buggy rsh min/max bounds tracking

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Fix incorrect bounds tracking for RSH opcode. Commit f23cc643f9 ("bpf: fix
range arithmetic for bpf map access") had a wrong assumption about min/max
bounds. The new dst_reg->min_value needs to be derived by right shifting the
max_val bounds, not min_val, and likewise new dst_reg->max_value needs to be
derived by right shifting the min_val bounds, not max_val. Later stable kernels
than 4.9 are not affected since bounds tracking was overall reworked and they
already track this similarly as in the fix.

Fixes: f23cc643f9 ("bpf: fix range arithmetic for bpf map access")
Reported-by: Ryota Shiga (Flatt Security)
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Cc: Josef Bacik <jbacik@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Borkmann 2021-01-22 16:00:56 +01:00 committed by Greg Kroah-Hartman
parent 20089f3284
commit b984811672
1 changed files with 3 additions and 4 deletions
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7
kernel/bpf/verifier.c
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@ -1732,12 +1732,11 @@ static void adjust_reg_min_max_vals(struct bpf_verifier_env *env,
* unsigned shift, so make the appropriate casts.
*/
if (min_val < 0 || dst_reg->min_value < 0)
dst_reg->min_value = BPF_REGISTER_MIN_RANGE;
reset_reg_range_values(regs, insn->dst_reg);
else
dst_reg->min_value =
(u64)(dst_reg->min_value) >> min_val;
dst_reg->min_value = (u64)(dst_reg->min_value) >> max_val;
if (dst_reg->max_value != BPF_REGISTER_MAX_RANGE)
dst_reg->max_value >>= max_val;
dst_reg->max_value >>= min_val;
break;
default:
reset_reg_range_values(regs, insn->dst_reg);