Staging: p9auth: a few fixes

1. The memory into which we copy 'u1@u2' needs space for u1, @,
	u2, and a final \0 which strcat copies in.
2. Strsep changes the value of its first argument.  So use a
	temporary variable to pass to it, so we pass the original
	value to kfree!
3. Allocate an extra char to user_buf, because we need a trailing \0
	since we later kstrdup it.

I am about to send out an LTP testcase for this driver, but
in addition the correctness of the hashing can be verified as
follows:

 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>

int main(int argc, char *argv[])
{
        char in[41], out[20];
        unsigned int v;
        int i, ret;

        ret = read(STDIN_FILENO, in, 40);
        if (ret != 40)
                exit(1);
        in[40] = '\0';
        for (i = 0; i < 20; i++) {
                sscanf(&in[2*i], "%02x", &v);
                out[i] = v;
        }
        write(STDOUT_FILENO, out, 20);
}

as root, to test userid 501 switching to uid 0, choosing
'random' string 'ab':

echo -n "501@0" > plain
openssl sha1  -hmac 'ab' plain |awk '{ print $2 '} > dgst
./unhex < dgst > dgst.u
mknod /dev/caphash 504 0
mknod /dev/capuse 504 1
chmod ugo+w /dev/capuse
cat dgst.u > /dev/caphash

as uid 501,
echo "501@0@ab" > /dev/capuse
id -u  # should now show 0.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 6 deletions

diff --git a/drivers/staging/p9auth/p9auth.c b/drivers/staging/p9auth/p9auth.c
index 9111dcba37a1..8ccfff723eec 100644
--- a/drivers/staging/p9auth/p9auth.c
+++ b/drivers/staging/p9auth/p9auth.c
@@ -183,7 +183,7 @@ static ssize_t cap_write(struct file *filp, const char __user *buf,
         user_buf_running = NULL;
         hash_str = NULL;
         node_ptr = kmalloc(sizeof(struct cap_node), GFP_KERNEL);
-        user_buf = kzalloc(count, GFP_KERNEL);
+        user_buf = kzalloc(count+1, GFP_KERNEL);
         if (!node_ptr || !user_buf)
                 goto out;
 
@@ -207,6 +207,7 @@ static ssize_t cap_write(struct file *filp, const char __user *buf,
                 list_add(&(node_ptr->list), &(dev->head->list));
                 node_ptr = NULL;
         } else {
+                char *tmpu;
                 if (!cap_devices[0].head ||
                                 list_empty(&(cap_devices[0].head->list))) {
                         retval = -EINVAL;
@@ -218,10 +219,10 @@ static ssize_t cap_write(struct file *filp, const char __user *buf,
                  * need to split it and hash 'user1@user2' using 'randomstring'
                  * as the key.
                  */
-                user_buf_running = kstrdup(user_buf, GFP_KERNEL);
-                source_user = strsep(&user_buf_running, "@");
-                target_user = strsep(&user_buf_running, "@");
-                rand_str = strsep(&user_buf_running, "@");
+                tmpu = user_buf_running = kstrdup(user_buf, GFP_KERNEL);
+                source_user = strsep(&tmpu, "@");
+                target_user = strsep(&tmpu, "@");
+                rand_str = tmpu;
                 if (!source_user || !target_user || !rand_str) {
                         retval = -EINVAL;
                         goto out;
@@ -229,7 +230,8 @@ static ssize_t cap_write(struct file *filp, const char __user *buf,
 
                 /* hash the string user1@user2 with rand_str as the key */
                 len = strlen(source_user) + strlen(target_user) + 1;
-                hash_str = kzalloc(len, GFP_KERNEL);
+                /* src, @, len, \0 */
+                hash_str = kzalloc(len+1, GFP_KERNEL);
                 strcat(hash_str, source_user);
                 strcat(hash_str, "@");
                 strcat(hash_str, target_user);