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.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>

diff --git a/mkfs.c b/mkfs.c
index 2ad180a13e58ccc75ba1ca89b422cc2ad0265b7c..2a11af5cfcdb64ea15eb01401c94497e37d57166 100644 (file)
--- a/mkfs.c
+++ b/mkfs.c
@@ -342,9 +342,9 @@ 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++) {