On Mon, 23 Oct 2017 22:07:41 +0530
"Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> 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:
> Reported-by: David Laight <david.lai...@aculab.com>
> Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> ---
> 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 <mhira...@kernel.org>
