From: Daniel Borkmann <daniel@iogearbox.net>
Date: Wed, 15 Dec 2021 22:28:48 +0000
Subject: bpf: Make 32->64 bounds propagation slightly more robust
Git-commit: e572ff80f05c33cd0cb4860f864f5c9c044280b6
Patch-mainline: v5.16-rc6
References: bsc#1196130,CVE-2021-45402

Make the bounds propagation in __reg_assign_32_into_64() slightly more
robust and readable by aligning it similarly as we did back in the
__reg_combine_64_into_32() counterpart. Meaning, only propagate or
pessimize them as a smin/smax pair.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Tony Jones <tonyj@suse.de>
---
 kernel/bpf/verifier.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0872b6c9fb33..b532f1058d35 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1366,22 +1366,28 @@ static void __reg_bound_offset(struct bpf_reg_state *reg)
 	reg->var_off = tnum_or(tnum_clear_subreg(var64_off), var32_off);
 }
 
+static bool __reg32_bound_s64(s32 a)
+{
+	return a >= 0 && a <= S32_MAX;
+}
+
 static void __reg_assign_32_into_64(struct bpf_reg_state *reg)
 {
 	reg->umin_value = reg->u32_min_value;
 	reg->umax_value = reg->u32_max_value;
-	/* Attempt to pull 32-bit signed bounds into 64-bit bounds
-	 * but must be positive otherwise set to worse case bounds
-	 * and refine later from tnum.
+
+	/* Attempt to pull 32-bit signed bounds into 64-bit bounds but must
+	 * be positive otherwise set to worse case bounds and refine later
+	 * from tnum.
 	 */
-	if (reg->s32_min_value >= 0 && reg->s32_max_value >= 0)
-		reg->smax_value = reg->s32_max_value;
-	else
-		reg->smax_value = U32_MAX;
-	if (reg->s32_min_value >= 0)
+	if (__reg32_bound_s64(reg->s32_min_value) &&
+	    __reg32_bound_s64(reg->s32_max_value)) {
 		reg->smin_value = reg->s32_min_value;
-	else
+		reg->smax_value = reg->s32_max_value;
+	} else {
 		reg->smin_value = 0;
+		reg->smax_value = U32_MAX;
+	}
 }
 
 static void __reg_combine_32_into_64(struct bpf_reg_state *reg)