The "buflen" value comes from the user and there is a potential that it could be zero. In do_handle_to_path() we know that "handle->handle_bytes" is non-zero and we do: handle_dwords = handle->handle_bytes >> 2; So values 1-3 become zero. Then in ovl_fh_to_dentry() we do: int len = fh_len << 2; So now len is in the "0,4-128" range and a multiple of 4. But if "buflen" is zero it will try to copy negative bytes when we do the memcpy in ovl_fid_to_fh(). memcpy(&fh->fb, fid, buflen - OVL_FH_WIRE_OFFSET); And that will lead to a crash. Thanks to Amir Goldstein for his help with this patch. Fixes: cbe7fba8edfc: ("ovl: make sure that real fid is 32bit aligned in memory") Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx> --- fs/overlayfs/export.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c index 475c61f53f0fe..0e58213ace6d7 100644 --- a/fs/overlayfs/export.c +++ b/fs/overlayfs/export.c @@ -776,6 +776,9 @@ static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type) { struct ovl_fh *fh; + if (buflen <= OVL_FH_WIRE_OFFSET) + return ERR_PTR(-EINVAL); + /* If on-wire inner fid is aligned - nothing to do */ if (fh_type == OVL_FILEID_V1) return (struct ovl_fh *)fid; -- 2.26.2