lseek: tighten error checking and allow negative offsets for SEEK_END

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/fs.c b/fs/fs.c
index e7b6965914..1901c94ad1 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -910,6 +910,8 @@ loff_t lseek(int fildes, loff_t offset, int whence)
 	case SEEK_SET:
 		if (f->size != FILE_SIZE_STREAM && offset > f->size)
 			goto out;
+		if (offset < 0)
+			goto out;
 		pos = offset;
 		break;
 	case SEEK_CUR:
@@ -918,9 +920,9 @@ loff_t lseek(int fildes, loff_t offset, int whence)
 		pos = f->pos + offset;
 		break;
 	case SEEK_END:
-		if (offset)
+		if (offset > 0)
 			goto out;
-		pos = f->size;
+		pos = f->size + offset;
 		break;
 	default:
 		goto out;