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Subject[PATCH v4 3/7] kprobes: validate the symbol name provided during probe registration
Date
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>
---
Masami, Michael,
Here's a simplified version that should hopefully be fine. I have
simplified the logic to keep the code compact and simple.

- Naveen


include/linux/kprobes.h | 1 +
kernel/kprobes.c | 30 ++++++++++++++++++++++++++++++
kernel/trace/trace_kprobe.c | 4 ++++
3 files changed, 35 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..ff9b1ac72a38 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1383,6 +1383,34 @@ bool within_kprobe_blacklist(unsigned long addr)
}

/*
+ * We mainly want to ensure that the provided string is of a reasonable length
+ * and is of the form [<mod_name>:]<sym_name>, so that this is safe to process
+ * further.
+ * We don't worry about invalid characters as those will just prevent
+ * matching existing kallsyms.
+ */
+bool is_valid_kprobe_symbol_name(const char *name)
+{
+ size_t sym_len;
+ const char *s;
+
+ s = strnchr(name, ':', MODULE_NAME_LEN + KSYM_NAME_LEN + 1);
+ if (s) {
+ sym_len = (size_t)(s - name);
+ if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
+ return false;
+ s++;
+ } else
+ s = name;
+
+ sym_len = strnlen(s, KSYM_NAME_LEN);
+ if (sym_len <= 0 || sym_len >= KSYM_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.
* This returns encoded errors if it fails to look up symbol or invalid
@@ -1397,6 +1425,8 @@ 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
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