Consolidate buffer length checking with new-line/end-of-line checking.
Additionally, instead of reading user memory twice, just do the assignment
during the loop.
This change doesn't affect the potential races here. It was already
possible to read a sysctl that was in the middle of a write. In both
cases, the string will always be NULL terminated. The pre-existing race
remains a problem to be solved.
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
kernel/sysctl.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e7ff80a73c44..0e08103a69c8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1712,21 +1712,18 @@ static int _proc_do_string(char *data, int maxlen, int write,
}
if (write) {
+ /* Start writing from beginning of buffer. */
len = 0;
+ *ppos += *lenp;
p = buffer;
- while (len < *lenp) {
+ while ((p - buffer) < *lenp && len < maxlen - 1) {
if (get_user(c, p++))
return -EFAULT;
if (c == 0 || c == '\n')
break;
- len++;
+ data[len++] = c;
}
- if (len >= maxlen)
- len = maxlen-1;
- if(copy_from_user(data, buffer, len))
- return -EFAULT;
data[len] = 0;
- *ppos += *lenp;
} else {
len = strlen(data);
if (len > maxlen)
--
1.7.9.5
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