linux-kernel - [PATCH 5.10 46/54] bpf: Fix verifier jsgt branch analysis on max bound

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Date:   Thu, 11 Feb 2021 16:02:30 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>
Subject: [PATCH 5.10 46/54] bpf: Fix verifier jsgt branch analysis on max bound

From: Daniel Borkmann <daniel@...earbox.net>

commit ee114dd64c0071500345439fc79dd5e0f9d106ed upstream.

Fix incorrect is_branch{32,64}_taken() analysis for the jsgt case. The return
code for both will tell the caller whether a given conditional jump is taken
or not, e.g. 1 means branch will be taken [for the involved registers] and the
goto target will be executed, 0 means branch will not be taken and instead we
fall-through to the next insn, and last but not least a -1 denotes that it is
not known at verification time whether a branch will be taken or not. Now while
the jsgt has the branch-taken case correct with reg->s32_min_value > sval, the
branch-not-taken case is off-by-one when testing for reg->s32_max_value < sval
since the branch will also be taken for reg->s32_max_value == sval. The jgt
branch analysis, for example, gets this right.

Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Fixes: 4f7b3e82589e ("bpf: improve verifier branch analysis")
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Reviewed-by: John Fastabend <john.fastabend@...il.com>
Acked-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/bpf/verifier.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6822,7 +6822,7 @@ static int is_branch32_taken(struct bpf_
 	case BPF_JSGT:
 		if (reg->s32_min_value > sval)
 			return 1;
-		else if (reg->s32_max_value < sval)
+		else if (reg->s32_max_value <= sval)
 			return 0;
 		break;
 	case BPF_JLT:
@@ -6895,7 +6895,7 @@ static int is_branch64_taken(struct bpf_
 	case BPF_JSGT:
 		if (reg->smin_value > sval)
 			return 1;
-		else if (reg->smax_value < sval)
+		else if (reg->smax_value <= sval)
 			return 0;
 		break;
 	case BPF_JLT: