linux-kernel - [PATCH] hfs: fix deadlock in hfs_extend

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Date: Tue,  2 Jan 2024 20:36:51 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+41a88b825a315aac2254@...kaller.appspotmail.com
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com,
	willy@...radead.org
Subject: [PATCH] hfs: fix deadlock in hfs_extend_file

[syz report]
syz-executor279/5059 is trying to acquire lock:
ffff888079c100f8 (&HFS_I(tree->inode)->extents_lock){+.+.}-{3:3}, at: hfs_extend_file+0xa2/0xb10 fs/hfs/extent.c:397

but task is already holding lock:
ffff888079c10778 (&HFS_I(tree->inode)->extents_lock){+.+.}-{3:3}, at: hfs_extend_file+0xa2/0xb10 fs/hfs/extent.c:397

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&HFS_I(tree->inode)->extents_lock);
  lock(&HFS_I(tree->inode)->extents_lock);

 *** DEADLOCK ***
[Analysis] 
 hfs_extend_file()->
   hfs_ext_read_extent()->
     __hfs_ext_cache_extent()->
       __hfs_ext_write_extent()->
         hfs_bmap_reserve()->
           hfs_extend_file()->

When an inode has both the HFS_FLG_EXT_DIRTY and HFS_FLG_EXT_NEW flags, it will
enter the above loop and trigger a deadlock.

[Fix]
In hfs_ext_read_extent(), check if the above two flags exist simultaneously, 
and exit the subsequent process when the conditions are met.

Reported-and-tested-by: syzbot+41a88b825a315aac2254@...kaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
 fs/hfs/extent.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/hfs/extent.c b/fs/hfs/extent.c
index 6d1878b99b30..1b02c7b6a10c 100644
--- a/fs/hfs/extent.c
+++ b/fs/hfs/extent.c
@@ -197,6 +197,10 @@ static int hfs_ext_read_extent(struct inode *inode, u16 block)
 	    block < HFS_I(inode)->cached_start + HFS_I(inode)->cached_blocks)
 		return 0;
 
+	if (HFS_I(inode)->flags & HFS_FLG_EXT_DIRTY && 
+	    HFS_I(inode)->flags & HFS_FLG_EXT_NEW) 
+		return -ENOENT;
+
 	res = hfs_find_init(HFS_SB(inode->i_sb)->ext_tree, &fd);
 	if (!res) {
 		res = __hfs_ext_cache_extent(&fd, inode, block);
-- 
2.43.0