linux-ext4 - [PATCH 5.4] ext4: fix race condition between ext4_ioctl_setflags and ext4

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Message-ID: <20220722073334.1893924-1-libaokun1@huawei.com>
Date:   Fri, 22 Jul 2022 15:33:34 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     <stable@...r.kernel.org>, <linux-ext4@...r.kernel.org>
CC:     <gregkh@...uxfoundation.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <jack@...e.cz>,
        <ritesh.list@...il.com>, <lczerner@...hat.com>,
        <enwlinux@...il.com>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>, <yebin10@...wei.com>, <yukuai3@...wei.com>,
        <libaokun1@...wei.com>, Hulk Robot <hulkci@...wei.com>
Subject: [PATCH 5.4] ext4: fix race condition between ext4_ioctl_setflags and ext4_fiemap

This patch and problem analysis is based on v4.19 LTS.
The d3b6f23f7167("ext4: move ext4_fiemap to use iomap framework") patch
is incorporated in v5.7-rc1. This patch avoids this problem by switching
to iomap in ext4_fiemap.

Hulk Robot reported a BUG on stable 4.19.252:
==================================================================
kernel BUG at fs/ext4/extents_status.c:762!
invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 7 PID: 2845 Comm: syz-executor Not tainted 4.19.252 #46
RIP: 0010:ext4_es_cache_extent+0x30e/0x370
[...]
Call Trace:
 ext4_cache_extents+0x238/0x2f0
 ext4_find_extent+0x785/0xa40
 ext4_fiemap+0x36d/0xe90
 do_vfs_ioctl+0x6af/0x1200
[...]
==================================================================

Above issue may happen as follows:
-------------------------------------
           cpu1		    cpu2
_____________________|_____________________
do_vfs_ioctl
 ext4_ioctl
  ext4_ioctl_setflags
   ext4_ind_migrate
                        do_vfs_ioctl
                         ioctl_fiemap
                          ext4_fiemap
                           ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)
                           ext4_fill_fiemap_extents
    down_write(&EXT4_I(inode)->i_data_sem);
    ext4_ext_check_inode
    ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS)
    memset(ei->i_data, 0, sizeof(ei->i_data))
    up_write(&EXT4_I(inode)->i_data_sem);
                            down_read(&EXT4_I(inode)->i_data_sem);
                            ext4_find_extent
                             ext4_cache_extents
                              ext4_es_cache_extent
                               BUG_ON(end < lblk)

We can easily reproduce this problem with the syzkaller testcase:
```
02:37:07 executing program 3:
r0 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file0\x00', 0x26e1, 0x0)
ioctl$FS_IOC_FSSETXATTR(r0, 0x40086602, &(0x7f0000000080)={0x17e})
mkdirat(0xffffffffffffff9c, &(0x7f00000000c0)='./file1\x00', 0x1ff)
r1 = openat(0xffffffffffffff9c, &(0x7f0000000100)='./file1\x00', 0x0, 0x0)
ioctl$FS_IOC_FIEMAP(r1, 0xc020660b, &(0x7f0000000180)={0x0, 0x1, 0x0, 0xef3, 0x6, []}) (async, rerun: 32)
ioctl$FS_IOC_FSSETXATTR(r1, 0x40086602, &(0x7f0000000140)={0x17e}) (rerun: 32)
```

To solve this issue, we use __generic_block_fiemap() instead of
generic_block_fiemap() and add inode_lock_shared to avoid race condition.

Reported-by: Hulk Robot <hulkci@...wei.com>
Signed-off-by: Baokun Li <libaokun1@...wei.com>
---
 fs/ext4/extents.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index f1bbce4350c4..50f956bda34c 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5175,16 +5175,21 @@ static int _ext4_fiemap(struct inode *inode,
 		fieinfo->fi_flags &= ~FIEMAP_FLAG_CACHE;
 	}
 
+	inode_lock_shared(inode);
 	/* fallback to generic here if not in extents fmt */
 	if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) &&
-	    fill == ext4_fill_fiemap_extents)
-		return generic_block_fiemap(inode, fieinfo, start, len,
+	    fill == ext4_fill_fiemap_extents) {
+		error = __generic_block_fiemap(inode, fieinfo, start, len,
 			ext4_get_block);
+		goto out_unlock;
+	}
 
 	if (fill == ext4_fill_es_cache_info)
 		ext4_fiemap_flags &= FIEMAP_FLAG_XATTR;
-	if (fiemap_check_flags(fieinfo, ext4_fiemap_flags))
-		return -EBADR;
+	if (fiemap_check_flags(fieinfo, ext4_fiemap_flags)) {
+		error = -EBADR;
+		goto out_unlock;
+	}
 
 	if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR) {
 		error = ext4_xattr_fiemap(inode, fieinfo);
@@ -5204,6 +5209,8 @@ static int _ext4_fiemap(struct inode *inode,
 		 */
 		error = fill(inode, start_blk, len_blks, fieinfo);
 	}
+out_unlock:
+	inode_unlock_shared(inode);
 	return error;
 }
 
-- 
2.31.1