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SubjectRe: [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in kprobe_lookup_name()
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On 04/21/2017 07:33 AM, Naveen N. Rao wrote:
> Convert usage of strchr()/strncpy()/strncat() to
> strnchr()/memcpy()/strlcat() for simpler and safer string manipulation.
>
> Reported-by: David Laight <David.Laight@ACULAB.COM>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> Changes: Additionally convert the strchr().
>
>
> arch/powerpc/kernel/kprobes.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 97b5eed1f76d..c73fb6e3b43f 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -65,28 +65,27 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
> char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
> const char *modsym;
> bool dot_appended = false;
> - if ((modsym = strchr(name, ':')) != NULL) {
> + if ((modsym = strnchr(name, ':', MODULE_NAME_LEN)) != NULL) {
> modsym++;
> if (*modsym != '\0' && *modsym != '.') {
> /* Convert to <module:.symbol> */
> - strncpy(dot_name, name, modsym - name);
> + memcpy(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);
> + strlcat(dot_name, modsym, sizeof(dot_name));

Would it be more efficient here to replace this:
--
dot_name[modsym - name + 1] = '\0';
strlcat(dot_name, modsym, sizeof(dot_name));
--

with this:
strncpy(&dot_name[modsym - name + 1], modsym, KSYM_NAME_LEN);

(So you aren't rescanning dot_name to find the end, when you already know the end position?)

> dot_appended = true;
> } else {
> dot_name[0] = '\0';
> - strncat(dot_name, name, sizeof(dot_name) - 1);
> + strlcat(dot_name, name, sizeof(dot_name));

and here do:
strncpy(dot_name, name, sizeof(dot_name));

(and remove the null termination immediately above)

> }
> } else if (name[0] != '.') {
> dot_name[0] = '.';
> dot_name[1] = '\0';
> - strncat(dot_name, name, KSYM_NAME_LEN - 2);
> + strlcat(dot_name, name, sizeof(dot_name));

and here do:
strncpy(&dot_name[1], name, sizeof(dot_name));

(and remove the null termination immediately above)

> dot_appended = true;
> } else {
> dot_name[0] = '\0';
> - strncat(dot_name, name, KSYM_NAME_LEN - 1);
> + strlcat(dot_name, name, sizeof(dot_name));

and here do:
strncpy(dot_name, name, sizeof(dot_name));

(and remove the null termination immediately above)

> }

PC

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