bpf: fix missing error return in check_stack_boundary()

thejh · borkmann · commit ea25f914dc16 · 2017-12-21T02:15:41.000+01:00
Prevent indirect stack accesses at non-constant addresses, which would permit reading and corrupting spilled pointers. Fixes: f1174f7 ("bpf/verifier: rework value tracking") Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
@@ -1303,6 +1303,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
 		tnum_strn(tn_buf, sizeof(tn_buf), regs[regno].var_off);
 		verbose(env, "invalid variable stack read R%d var_off=%s\n",
 			regno, tn_buf);
+		return -EACCES;
 	}
 	off = regs[regno].off + regs[regno].var_off.value;
 	if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||

Original file line number	Diff line number	Diff line change
`@@ -1303,6 +1303,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,`
`1303`	`1303`	`tnum_strn(tn_buf, sizeof(tn_buf), regs[regno].var_off);`
`1304`	`1304`	`verbose(env, "invalid variable stack read R%d var_off=%s\n",`
`1305`	`1305`	`regno, tn_buf);`
	`1306`	`+ return -EACCES;`
`1306`	`1307`	`}`
`1307`	`1308`	`off = regs[regno].off + regs[regno].var_off.value;`
`1308`	`1309`	`if (off >= 0 \|\| off < -MAX_BPF_STACK \|\| off + access_size > 0 \|\|`