zonefs: handle integer overflow in zonefs_fname_to_fno

[ Upstream commit 3a8389d42b ]

In zonefs the file name in one of the two directories corresponds to the
zone number.

Here Alexey reported a possible integer overflow in zonefs_fname_to_fno(),
where the parsing of the zone number from the file name can overflow the
'long' data type.

Add a check for integer overflows and if the fno 'long' did overflow
return -ENOENT.

Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Fixes: d207794aba ("zonefs: Dynamically create file inodes when needed")
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/zonefs/super.c

@@ -610,10 +610,14 @@ static long zonefs_fname_to_fno(const struct qstr *fname)
 		return c - '0';
 
 	for (i = 0, rname = name + len - 1; i < len; i++, rname--) {
+		long digit;
+
 		c = *rname;
 		if (!isdigit(c))
 			return -ENOENT;
-		fno += (c - '0') * shift;
+		digit = (c - '0') * shift;
+		if (check_add_overflow(fno, digit, &fno))
+			return -ENOENT;
 		shift *= 10;
 	}