[rtems commit] libfdt: fix undefined behaviour in fdt_splice_()

[Sebastian Huber]

Module:    rtems
Branch:    master
Commit:    caa59e66fdf3b7da52282e3b334d6e6ae00f4292
Changeset: http://git.rtems.org/rtems/commit/?id=caa59e66fdf3b7da52282e3b334d6e6ae00f4292

Author:    Jan Beulich <jbeulich at suse.com>
Date:      Thu Mar  5 15:04:45 2020 +0100

libfdt: fix undefined behaviour in fdt_splice_()

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. (The left side of the checks added by
d4c7c25c9ed1 ["libfdt: check for potential overrun in _fdt_splice()"]
doesn't really lend itself to similar replacement though.)

Signed-off-by: Jan Beulich <jbeulich at suse.com>
Message-Id: <f2d09e81-7cb8-c5cc-9699-1ac05b0626ff at suse.com>
Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

---

 cpukit/dtc/libfdt/fdt_rw.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/cpukit/dtc/libfdt/fdt_rw.c b/cpukit/dtc/libfdt/fdt_rw.c
index 1385425..524b520 100644
--- a/cpukit/dtc/libfdt/fdt_rw.c
+++ b/cpukit/dtc/libfdt/fdt_rw.c
@@ -46,7 +46,7 @@ static int fdt_rw_probe_(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);
 }
@@ -54,15 +54,16 @@ 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 ((p < (char *)fdt) || ((end - oldlen + newlen) < (char *)fdt))
+	if ((p < (char *)fdt) || (dsize + newlen < oldlen))
 		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;
 }