Re: [PATCH] btrfs: fix oob Read in getname_kernel

David Sterba
2024-01-10T15:56:08Z

On Tue, Dec 19, 2023 at 06:19:10PM +0800, Edward Adam Davis wrote:
> If ioctl does not pass in the correct tgtdev_name string, oob will occur because
> "\0" cannot be found.
>
> Reported-and-tested-by: syzbot+33f23b49ac24f986c9e8@syzkaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> fs/btrfs/dev-replace.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
> index f9544fda38e9..e7e96e57f682 100644
> --- a/fs/btrfs/dev-replace.c
> +++ b/fs/btrfs/dev-replace.c
> @@ -730,7 +730,7 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
> int btrfs_dev_replace_by_ioctl(struct btrfs_fs_info *fs_info,
> struct btrfs_ioctl_dev_replace_args *args)
> {
> - int ret;
> + int ret, len;
>
> switch (args->start.cont_reading_from_srcdev_mode) {
> case BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_ALWAYS:
> @@ -740,8 +740,10 @@ int btrfs_dev_replace_by_ioctl(struct btrfs_fs_info *fs_info,
> return -EINVAL;
> }
>
> + len = strnlen(args->start.tgtdev_name, BTRFS_DEVICE_PATH_NAME_MAX + 1);
> if ((args->start.srcdevid == 0 && args->start.srcdev_name[0] == '\0') ||
> - args->start.tgtdev_name[0] == '\0')
> + args->start.tgtdev_name[0] == '\0' ||
> + len == BTRFS_DEVICE_PATH_NAME_MAX + 1)

I think srcdev_name would have to be checked the same way, but instead
of strnlen I'd do memchr(name, 0, BTRFS_DEVICE_PATH_NAME_MAX). The check
for 0 in [0] is probably pointless, it's just a shortcut for an empty
buffer. We expect a valid 0-terminated string, which could be an invalid
path but that will be found out later when opening the block device.