[PATCH v2] cifs: small underflow in cnvrtDosUnixTm()

Dan Carpenter
2017-04-28T12:51:30Z

January is month 1. There is no zero-th month. If someone passes a
zero month then it means we read from one space before the start of the
total_days_of_prev_months[] array.

We may as well also be strict about days as well.

Fixes: 1bd5bbcb6531 ("[CIFS] Legacy time handling for Win9x and OS/2 part 1")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
v2: Be strict about days as well. My first patch was less intrusive
because it only prevented the out of bounds access. I have no idea how
common it is to pass in an illegal day but, hopefully, not very common.

diff --git a/fs/cifs/netmisc.c b/fs/cifs/netmisc.c
index abae6dd2c6b9..4b2726ee4fad 100644
--- a/fs/cifs/netmisc.c
+++ b/fs/cifs/netmisc.c
@@ -980,10 +980,10 @@ struct timespec cnvrtDosUnixTm(__le16 le_date, __le16 le_time, int offset)
cifs_dbg(VFS, "illegal hours %d\n", st->Hours);
days = sd->Day;
month = sd->Month;
- if ((days > 31) || (month > 12)) {
+ if (days < 1 || days > 31 || month < 1 || month > 12) {
cifs_dbg(VFS, "illegal date, month %d day: %d\n", month, days);
- if (month > 12)
- month = 12;
+ days = (days < 1) ? 1 : ((days <= 31) ? days : 31);
+ month = (month < 1) ? 1 : ((month <= 12) ? month : 12);
}
month -= 1;
days += total_days_of_prev_months[month];