use use SEEK_MAX to validate user lseek arguments

Add SEEK_MAX and use it to validate lseek arguments from userspace.
Signed-off-by: NChris Snook <csnook@redhat.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/read_write.c

@@ -139,7 +139,7 @@ asmlinkage off_t sys_lseek(unsigned int fd, off_t offset, unsigned int origin)
 		goto bad;
 
 	retval = -EINVAL;
-	if (origin <= 2) {
+	if (origin <= SEEK_MAX) {
 		loff_t res = vfs_llseek(file, offset, origin);
 		retval = res;
 		if (res != (loff_t)retval)
@@ -166,7 +166,7 @@ asmlinkage long sys_llseek(unsigned int fd, unsigned long offset_high,
 		goto bad;
 
 	retval = -EINVAL;
-	if (origin > 2)
+	if (origin > SEEK_MAX)
 		goto out_putf;
 
 	offset = vfs_llseek(file, ((loff_t) offset_high << 32) | offset_low,

include/linux/fs.h

@@ -30,6 +30,7 @@
 #define SEEK_SET	0	/* seek relative to beginning of file */
 #define SEEK_CUR	1	/* seek relative to current file position */
 #define SEEK_END	2	/* seek relative to end of file */
+#define SEEK_MAX	SEEK_END
 
 /* And dynamically-tunable limits and defaults: */
 struct files_stat_struct {