Excerpts from Masami Hiramatsu's message of April 19, 2017 20:07:

On Wed, 19 Apr 2017 18:21:02 +0530
"Naveen N. Rao" [off-list ref] wrote:
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quoted

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.

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Would we really need this? Of course it may filter out longer
strings... anyway such name should be rejected by kallsyms.

I felt this would be good to have generically, as kallsyms does many=20
string operations on the symbol name, including an unbounded strchr().

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[...]

quoted

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;
 }

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+bool is_valid_kprobe_symbol_name(const char *name)

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This just check the length of symbol_name buffer, and can contain
some invalid chars.

Yes, I kept the function name generic incase we would like to do more=20
validation in future, plus it's shorter than=20
is_valid_kprobe_symbol_name_len() ;-)

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quoted

+{
+	size_t sym_len;
+	char *s;
+
+	s =3D strchr(name, ':');

Hmm.. this should be strnchr(). I re-factored the code that moved the=20
strnlen() above this below. I'll fix this.

quoted

+	if (s) {
+		sym_len =3D strnlen(s+1, KSYM_NAME_LEN);

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If you use strnlen() here, you just need to ensure sym_len < KSYM_NAME_LE=

N.

Hmm.. not sure I follow. Are you saying the check for sym_len <=3D 0 is=20
not needed?

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quoted

+		if (sym_len <=3D 0 || sym_len >=3D KSYM_NAME_LEN)
+			return false;
+		sym_len =3D (size_t)(s - name);
+		if (sym_len <=3D 0 || sym_len >=3D MODULE_NAME_LEN)
+			return false;
+	} else {
+		sym_len =3D strnlen(name, MODULE_NAME_LEN);
+		if (sym_len <=3D 0 || sym_len >=3D MODULE_NAME_LEN)

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Would you mean KSYM_NAME_LEN here?

Oops... nice catch, Thanks!

- Naveen

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quoted

+			return false;
+	}
+
+	return true;
+}
+
 /*
  * If we have a symbol_name argument, look it up and add the offset fie=

ld

quoted

  * 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)

quoted

 		goto invalid;
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 	if (p->symbol_name) {
+		if (!is_valid_kprobe_symbol_name(p->symbol_name))
+			return ERR_PTR(-EINVAL);
 		addr =3D 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 **arg=

v)

quoted

 			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 -=3D 2; argv +=3D 2;
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2.12.1
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Thanks,
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Masami Hiramatsu [off-list ref]
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