linux-kernel - [PATCH 4/4] file: Fix file descriptor leak in copy_fd

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Date:   Sat, 26 Mar 2022 14:40:09 +0300
From:   Fedor Pchelkin <aissur0002@...il.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Fedor Pchelkin <aissur0002@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: [PATCH 4/4] file: Fix file descriptor leak in copy_fd_bitmaps()

If count argument in copy_fd_bitmaps() is not a multiple of
BITS_PER_BYTE, then one byte is lost and is not used in further
manipulations with cpy value in memcpy() and memset()
causing a leak. The leak was introduced with close_range() call
using CLOSE_RANGE_UNSHARE flag.

The patch suggests implementing an indicator (named add_byte)
of count being multiple of BITS_PER_BYTE and adding it to the
cpy value.

Found by Syzkaller (https://github.com/google/syzkaller).

Signed-off-by: Fedor Pchelkin <aissur0002@...il.com>
Signed-off-by: Alexey Khoroshilov <khoroshilov@...ras.ru>
---
 fs/file.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 3ef1479df203..3c64a6423604 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -56,10 +56,8 @@ static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
 {
 	unsigned int cpy, set;
 	unsigned int add_byte = 0;
-	
 	if (count % BITS_PER_BYTE != 0)
 		add_byte = 1;
-	
 	cpy = count / BITS_PER_BYTE + add_byte;
 	set = (nfdt->max_fds - count) / BITS_PER_BYTE;
 	memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
-- 
2.25.1