[PATCH/mtd-utils] fix integer underflow in jffs2_rtime_compress()

[Enrico Scholz]

When '*dstlen' is 0 or 1, comparison will return wrong result.  Reported
by valgrind as

==5919== Invalid write of size 1
==5919==    at 0x40564E: jffs2_rtime_compress (compr_rtime.c:51)
==5919==    by 0x40676B: jffs2_compress (compr.c:246)
==5919==    by 0x403EE4: recursive_populate_directory (mkfs.jffs2.c:884)
==5919==  Address 0x4e1bdb1 is 0 bytes after a block of size 1 alloc'd
==5919==    at 0x4A0515D: malloc (vg_replace_malloc.c:195)
==5919==    by 0x40671C: jffs2_compress (compr.c:229)
==5919==    by 0x403EE4: recursive_populate_directory (mkfs.jffs2.c:884)

Signed-off-by: Enrico Scholz <enrico.scholz at sigma-chemnitz.de>
---
 compr_rtime.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/compr_rtime.c b/compr_rtime.c
index 131536c..5613963 100644
--- a/compr_rtime.c
+++ b/compr_rtime.c
@@ -32,7 +32,7 @@ static int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out
 
 	memset(positions,0,sizeof(positions));
 
-	while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
+	while (pos < (*sourcelen) && outpos+2 <= (*dstlen)) {
 		int backpos, runlen=0;
 		unsigned char value;
 
-- 
1.7.0.1