libfdt: fix undefined behaviour in _fdt_splice()

Along the lines of commit d0b3ab0a0f46 ("libfdt: Fix undefined behaviour
in fdt_offset_ptr()"), _fdt_splice() similarly may not use pointer
arithmetic to do overflow checks.

[upstream commit 73d6e9ecb4179b510408bc526240f829262df361]
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>

diff --git a/xen/common/libfdt/fdt_rw.c b/xen/common/libfdt/fdt_rw.c
index ee18bfc29857631241a43ac7525947fff19e68fe..8b8cd25cc20fc4b40e7bb52659efb27714ea7c4c 100644 (file)
--- a/xen/common/libfdt/fdt_rw.c
+++ b/xen/common/libfdt/fdt_rw.c
@@ -87,7 +87,7 @@ static int _fdt_rw_check_header(void *fdt)
                        return err; \
        }
 
-static inline int _fdt_data_size(void *fdt)
+static inline unsigned int _fdt_data_size(void *fdt)
 {
        return fdt_off_dt_strings(fdt) + fdt_size_dt_strings(fdt);
 }
@@ -95,13 +95,14 @@ static inline int _fdt_data_size(void *fdt)
 static int _fdt_splice(void *fdt, void *splicepoint, int oldlen, int newlen)
 {
        char *p = splicepoint;
-       char *end = (char *)fdt + _fdt_data_size(fdt);
+       unsigned int dsize = _fdt_data_size(fdt);
+       size_t soff = p - (char *)fdt;
 
-       if (((p + oldlen) < p) || ((p + oldlen) > end))
+       if (oldlen < 0 || soff + oldlen < soff || soff + oldlen > dsize)
                return -FDT_ERR_BADOFFSET;
-       if ((end - oldlen + newlen) > ((char *)fdt + fdt_totalsize(fdt)))
+       if (dsize - oldlen + newlen > fdt_totalsize(fdt))
                return -FDT_ERR_NOSPACE;
-       memmove(p + newlen, p + oldlen, end - p - oldlen);
+       memmove(p + newlen, p + oldlen, ((char *)fdt + dsize) - (p + oldlen));
        return 0;
 }