[PATCH] fs: fix d_path() with zero-length input buffer

[Denys Vlasenko <dvlasenk@redhat.com>]

In prepend_name(), *buflen < dlen + 1 comparison is buggy
because dlen has unsigned data type, and we can reach this location
with *buflen == -1.

The fix casts dlen to int.

Bug reports:
https://bugzilla.redhat.com/show_bug.cgi?id=1050964
https://bugzilla.redhat.com/show_bug.cgi?id=1060384

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Amerigo Wang <amwang@redhat.com>
Cc: "Jonathan M. Foote" <jmfoote@cert.org>
Cc: Roland McGrath <roland@hack.frob.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
---
 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 265e0ce..40ded0c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2833,7 +2833,7 @@ static int prepend_name(char **buffer, int *buflen, struct qstr *name)
 	u32 dlen = ACCESS_ONCE(name->len);
 	char *p;
 
-	if (*buflen < dlen + 1)
+	if (*buflen < (int)dlen + 1)
 		return -ENAMETOOLONG;
 	*buflen -= dlen + 1;
 	p = *buffer -= dlen + 1;
-- 
1.8.1.4