Btrfs-progs: specify label length larger than 255 bytes cause mkfs.btrfs buffer overflow

Hello,

While going through the mkfs.c, I noticed there is an issue for label length checking, mkfs.btrfs will crashed if the label length exceeding 255 bytes, it's easy to triggered that out as below:

jeff@pibroch:~/opensource/btrfs-progs$ sudo ./mkfs.btrfs -L `perl -e 'print "A"x256'` /usr/src/linux-3.0/img0

WARNING! - Btrfs v0.19-35-g1b444cd IS EXPERIMENTAL WARNING! - see http://btrfs.wiki.kernel.org before using

*** buffer overflow detected ***: ./mkfs.btrfs terminated ======= Backtrace: ========= /lib/i386-linux-gnu/libc.so.6(__fortify_fail+0x50)[0xb7774df0] /lib/i386-linux-gnu/libc.so.6(+0xe4cca)[0xb7773cca] /lib/i386-linux-gnu/libc.so.6(__strcpy_chk+0x3f)[0xb777305f] ./mkfs.btrfs[0x805acc4]
./mkfs.btrfs[0x805def6] /lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0xb76a5e37] ./mkfs.btrfs[0x8048ef1]
======= Memory map: ========
......

a tiny patch could fix it.

---
 mkfs.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

index 2e99b95..1598aae 100644
@@ -308,9 +308,9 @@ static char *parse_label(char *input)
     int i;
     int len = strlen(input);
 
-    if (len > BTRFS_LABEL_SIZE) {
+    if (len >= BTRFS_LABEL_SIZE) {
         fprintf(stderr, "Label %s is too long (max %d)\n", input,
-            BTRFS_LABEL_SIZE);
+            BTRFS_LABEL_SIZE - 1);
         exit(1);
     }
     for (i = 0; i < len; i++) {

1.7.4.1