[PATCH v3 3/7] kprobes: validate the symbol name length

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

When a kprobe is being registered, we use the symbol_name field to
lookup the address where the probe should be placed. Since this is a
user-provided field, let's ensure that the length of the string is
within expected limits.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 include/linux/kprobes.h     |  1 +
 kernel/kprobes.c            | 24 ++++++++++++++++++++++++
 kernel/trace/trace_kprobe.c |  4 ++++
 3 files changed, 29 insertions(+)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 1f82a3db00b1..4ee10fef5135 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -405,6 +405,7 @@ int disable_kprobe(struct kprobe *kp);
 int enable_kprobe(struct kprobe *kp);
 
 void dump_kprobe(struct kprobe *kp);
+bool is_valid_kprobe_symbol_name(const char *name);
 
 #else /* !CONFIG_KPROBES: */
 
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 6a128f3a7ed1..bb86681c8a10 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1382,6 +1382,28 @@ bool within_kprobe_blacklist(unsigned long addr)
 	return false;
 }
 
+bool is_valid_kprobe_symbol_name(const char *name)
+{
+	size_t sym_len;
+	char *s;
+
+	s = strchr(name, ':');
+	if (s) {
+		sym_len = strnlen(s+1, KSYM_NAME_LEN);
+		if (sym_len <= 0 || sym_len >= KSYM_NAME_LEN)
+			return false;
+		sym_len = (size_t)(s - name);
+		if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
+			return false;
+	} else {
+		sym_len = strnlen(name, MODULE_NAME_LEN);
+		if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
+			return false;
+	}
+
+	return true;
+}
+
 /*
  * If we have a symbol_name argument, look it up and add the offset field
  * to it. This way, we can specify a relative address to a symbol.
@@ -1397,6 +1419,8 @@ static kprobe_opcode_t *kprobe_addr(struct kprobe *p)
 		goto invalid;
 
 	if (p->symbol_name) {
+		if (!is_valid_kprobe_symbol_name(p->symbol_name))
+			return ERR_PTR(-EINVAL);
 		addr = kprobe_lookup_name(p->symbol_name, p->offset);
 		if (!addr)
 			return ERR_PTR(-ENOENT);
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 5f688cc724f0..bf73e5f31128 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -704,6 +704,10 @@ static int create_trace_kprobe(int argc, char **argv)
 			pr_info("Return probe must be used without offset.\n");
 			return -EINVAL;
 		}
+		if (!is_valid_kprobe_symbol_name(symbol)) {
+			pr_info("Symbol name is too long.\n");
+			return -EINVAL;
+		}
 	}
 	argc -= 2; argv += 2;
 
-- 
2.12.1