[PATCH] jffs2: Fix integer underflow in jffs2_rtime_compress

[Richard Weinberger]

The rtime compressor assumes that at least two bytes are
compressed.
If we try to compress just one byte, the loop condition will
wrap around and an out-of-bounds write happens.

Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Richard Weinberger <richard@xxxxxx>
---
 fs/jffs2/compr_rtime.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/jffs2/compr_rtime.c b/fs/jffs2/compr_rtime.c
index 406d9cc84ba8..cbf700001fc9 100644
--- a/fs/jffs2/compr_rtime.c
+++ b/fs/jffs2/compr_rtime.c
@@ -39,6 +39,9 @@ static int jffs2_rtime_compress(unsigned char *data_in,
 
 	memset(positions,0,sizeof(positions));
 
+	if (*dstlen < 2)
+		return -1;
+
 	while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
 		int backpos, runlen=0;
 		unsigned char value;
-- 
2.20.0