btrfs-progs: utils: make sure set_label_mounted uses correct length buffers

When `btrfs filesystem label /foo bar` command is invoked, it will pass
the buffer allocated in the argv array directly to set_label_mounted()
and then to the BTRFS_IOC_SET_FSLABEL ioctl.

However, the kernel code handling the ioctl will always try to copy
BTRFS_LABEL_SIZE bytes[1] from the userland pointer. Under certain
conditions and when the label is small enough, the command will fail
with:

    [root@localhost /]# btrfs filesystem label /mnt f
    ERROR: unable to set label Bad address

Fix this by making sure we pass a BTRFS_LABEL_SIZE sized buffer to the
ioctl containing the desired label.

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/ioctl.c?id=refs/tags/v4.5#n5231

Signed-off-by: Petros Angelatos <petrosagg@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/utils.c b/utils.c
index c0c564e..6602472 100644 (file)
--- a/utils.c
+++ b/utils.c
@@ -1755,9 +1755,10 @@ static int set_label_unmounted(const char *dev, const char *label)
        return 0;
 }
 
-static int set_label_mounted(const char *mount_path, const char *label)
+static int set_label_mounted(const char *mount_path, const char *labelp)
 {
        int fd;
+       char label[BTRFS_LABEL_SIZE];
 
        fd = open(mount_path, O_RDONLY | O_NOATIME);
        if (fd < 0) {
@@ -1765,6 +1766,8 @@ static int set_label_mounted(const char *mount_path, const char *label)
                return -1;
        }
 
+       memset(label, 0, sizeof(label));
+       strncpy(label, labelp, sizeof(label));
        if (ioctl(fd, BTRFS_IOC_SET_FSLABEL, label) < 0) {
                fprintf(stderr, "ERROR: unable to set label %s\n",
                        strerror(errno));