linux-ext4 - [PATCH] ext4: fix integer overflow when calculating commit interval

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Date:   Mon, 26 Aug 2019 22:35:47 +0800
From:   "zhangyi (F)" <yi.zhang@...wei.com>
To:     <linux-ext4@...r.kernel.org>
CC:     <tytso@....edu>, <jack@...e.cz>, <adilger.kernel@...ger.ca>,
        <yi.zhang@...wei.com>
Subject: [PATCH] ext4: fix integer overflow when calculating commit interval

If user specify a large enough value of "commit=" option, it may trigger
signed integer overflow which may lead to sbi->s_commit_interval becomes
a large or small value, zero in particular.

UBSAN: Undefined behaviour in ../fs/ext4/super.c:1592:31
signed integer overflow:
536870912 * 1000 cannot be represented in type 'int'
[...]
Call trace:
[...]
[<ffffff9008a2d120>] ubsan_epilogue+0x34/0x9c lib/ubsan.c:166
[<ffffff9008a2d8b8>] handle_overflow+0x228/0x280 lib/ubsan.c:197
[<ffffff9008a2d95c>] __ubsan_handle_mul_overflow+0x4c/0x68 lib/ubsan.c:218
[<ffffff90086d070c>] handle_mount_opt fs/ext4/super.c:1592 [inline]
[<ffffff90086d070c>] parse_options+0x1724/0x1a40 fs/ext4/super.c:1773
[<ffffff90086d51c4>] ext4_remount+0x2ec/0x14a0 fs/ext4/super.c:4834
[...]

Although it is not a big deal, still silence the UBSAN by limit the
input value.

Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>
---
 fs/ext4/super.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4079605d437a..7310facffa9d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1874,6 +1874,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
 	} else if (token == Opt_commit) {
 		if (arg == 0)
 			arg = JBD2_DEFAULT_MAX_COMMIT_AGE;
+		else if (arg > INT_MAX / HZ) {
+			ext4_msg(sb, KERN_ERR,
+				 "Invalid commit interval %d, "
+				 "must be smaller than %d",
+				 arg, INT_MAX / HZ);
+			return -1;
+		}
 		sbi->s_commit_interval = HZ * arg;
 	} else if (token == Opt_debug_want_extra_isize) {
 		sbi->s_want_extra_isize = arg;
-- 
2.23.0.rc2.8.gff66981