Re: [PATCH 4/4] powerpc/kprobes: refactor kprobe_lookup_name for safer string operations
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: 2017-10-25 16:35:57
On Mon, 23 Oct 2017 22:07:41 +0530 "Naveen N. Rao" [off-list ref] wrote:
Use safer string manipulation functions when dealing with a user-provided string in kprobe_lookup_name().
What would you mean "safer" here? using strnchr()? Could you please show at least an example case that causes problem in original code. And have one comment below:
quoted hunk ↗ jump to hunk
Reported-by: David Laight <redacted> Signed-off-by: Naveen N. Rao <redacted> --- arch/powerpc/kernel/kprobes.c | 47 ++++++++++++++++++------------------------- 1 file changed, 20 insertions(+), 27 deletions(-)diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index a14c61855705..bbb4795660f8 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c@@ -53,7 +53,7 @@ bool arch_within_kprobe_blacklist(unsigned long addr) kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) { - kprobe_opcode_t *addr; + kprobe_opcode_t *addr = NULL; #ifdef PPC64_ELF_ABI_v2 /* PPC64 ABIv2 needs local entry point */@@ -85,36 +85,29 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) * Also handle <module:symbol> format. */ char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN]; - const char *modsym; bool dot_appended = false; - if ((modsym = strchr(name, ':')) != NULL) { - modsym++; - if (*modsym != '\0' && *modsym != '.') { - /* Convert to <module:.symbol> */ - strncpy(dot_name, name, modsym - name); - dot_name[modsym - name] = '.'; - dot_name[modsym - name + 1] = '\0'; - strncat(dot_name, modsym, - sizeof(dot_name) - (modsym - name) - 2); - dot_appended = true; - } else { - dot_name[0] = '\0'; - strncat(dot_name, name, sizeof(dot_name) - 1); - } - } else if (name[0] != '.') { - dot_name[0] = '.'; - dot_name[1] = '\0'; - strncat(dot_name, name, KSYM_NAME_LEN - 2); + const char *c; + ssize_t ret = 0; + int len = 0; + + if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) { + c++; + len = c - name; + memcpy(dot_name, name, len); + } else + c = name; + + if (*c != '\0' && *c != '.') { + dot_name[len++] = '.'; dot_appended = true;
It is odd, you can call kallsyms_lookup_name(dot_name) here.
- } else {
- dot_name[0] = '\0';
- strncat(dot_name, name, KSYM_NAME_LEN - 1);
}
- addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
- if (!addr && dot_appended) {
- /* Let's try the original non-dot symbol lookup */
+ ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
+ if (ret > 0)
+ addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
+
+ /* Fallback to the original non-dot symbol lookup */
+ if (!addr && dot_appended)
addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);Then we can remove dot_appended. Thank you,
- } #else addr = (kprobe_opcode_t *)kallsyms_lookup_name(name); #endif -- 2.14.2
-- Masami Hiramatsu [off-list ref]