[PATCH] bpf: core: fix shift-out-of-bounds in ___bpf_prog_run

Kurt Manucredo fuzzybritches0 at gmail.com
Wed May 26 21:40:27 UTC 2021


Fix shift-out-of-bounds in ___bpf_prog_run().

UBSAN: shift-out-of-bounds in kernel/bpf/core.c:1414:2
shift exponent 248 is too large for 32-bit type 'unsigned int'
https://syzkaller.appspot.com/bug?id=edb51be4c9a320186328893287bb30d5eed09231

Reported-by: syzbot+bed360704c521841c85d at syzkaller.appspotmail.com
Signed-off-by: Kurt Manucredo <fuzzybritches0 at gmail.com>
---
 kernel/bpf/core.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5e31ee9f7512..35cba247c531 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1411,11 +1411,38 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
 	ALU(SUB,  -)
 	ALU(AND,  &)
 	ALU(OR,   |)
-	ALU(LSH, <<)
-	ALU(RSH, >>)
 	ALU(XOR,  ^)
 	ALU(MUL,  *)
 #undef ALU
+#define ALU(OPCODE, OP)		\
+	ALU64_##OPCODE##_X:		\
+		if (SRC >= 64)		\
+			DST = 0;	\
+		else			\
+			DST = DST OP SRC;	\
+		CONT;			\
+	ALU_##OPCODE##_X:		\
+		if (SRC >= 32)		\
+			DST = 0;	\
+		else			\
+			DST = (u32) DST OP (u32) SRC;	\
+		CONT;			\
+	ALU64_##OPCODE##_K:		\
+		if (IMM >= 64)		\
+			DST = 0;	\
+		else			\
+			DST = DST OP IMM;	\
+		CONT;			\
+	ALU_##OPCODE##_K:		\
+		if (IMM >= 32)		\
+			DST = 0;	\
+		else			\
+			DST = (u32) DST OP (u32) IMM;	\
+		CONT;
+
+	ALU(LSH, <<)
+	ALU(RSH, >>)
+#undef ALU
 	ALU_NEG:
 		DST = (u32) -DST;
 		CONT;
-- 
2.30.2



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