Patch "f2fs: fix to avoid potential deadlock" has been added to the 6.2-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    f2fs: fix to avoid potential deadlock

to the 6.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     f2fs-fix-to-avoid-potential-deadlock.patch
and it can be found in the queue-6.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d2b83e905c2dbae895d5563fa19f55fba10d8ed7
Author: Chao Yu <chao@xxxxxxxxxx>
Date:   Fri Dec 16 23:50:00 2022 +0800

    f2fs: fix to avoid potential deadlock
    
    [ Upstream commit 5eaac835f27f2de6b73412d7c24e755733b49de0 ]
    
    There is a potential deadlock reported by syzbot as below:
    
    F2FS-fs (loop2): invalid crc value
    F2FS-fs (loop2): Found nat_bits in checkpoint
    F2FS-fs (loop2): Mounted with checkpoint version = 48b305e4
    ======================================================
    WARNING: possible circular locking dependency detected
    6.1.0-rc8-syzkaller-33330-ga5541c0811a0 #0 Not tainted
    ------------------------------------------------------
    syz-executor.2/32123 is trying to acquire lock:
    ffff0000c0e1a608 (&mm->mmap_lock){++++}-{3:3}, at: __might_fault+0x54/0xb4 mm/memory.c:5644
    
    but task is already holding lock:
    ffff0001317c6088 (&sbi->sb_lock){++++}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2205 [inline]
    ffff0001317c6088 (&sbi->sb_lock){++++}-{3:3}, at: f2fs_ioc_get_encryption_pwsalt fs/f2fs/file.c:2334 [inline]
    ffff0001317c6088 (&sbi->sb_lock){++++}-{3:3}, at: __f2fs_ioctl+0x1370/0x3318 fs/f2fs/file.c:4151
    
    which lock already depends on the new lock.
    
    Chain exists of:
      &mm->mmap_lock --> &nm_i->nat_tree_lock --> &sbi->sb_lock
    
     Possible unsafe locking scenario:
    
           CPU0                    CPU1
           ----                    ----
      lock(&sbi->sb_lock);
                                   lock(&nm_i->nat_tree_lock);
                                   lock(&sbi->sb_lock);
      lock(&mm->mmap_lock);
    
    Let's try to avoid above deadlock condition by moving __might_fault()
    out of sbi->sb_lock coverage.
    
    Fixes: 95fa90c9e5a7 ("f2fs: support recording errors into superblock")
    Link: https://lore.kernel.org/linux-f2fs-devel/000000000000cd5fe305ef617fe2@xxxxxxxxxx/T/#u
    Reported-by: syzbot+4793f6096d174c90b4f7@xxxxxxxxxxxxxxxxxxxxxxxxx
    Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
    Reviewed-by: Eric Biggers <ebiggers@xxxxxxxxxx>
    Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ecbc8c135b494..2498e5c70fd83 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2338,6 +2338,7 @@ static int f2fs_ioc_get_encryption_pwsalt(struct file *filp, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	u8 encrypt_pw_salt[16];
 	int err;
 
 	if (!f2fs_sb_has_encrypt(sbi))
@@ -2362,12 +2363,14 @@ static int f2fs_ioc_get_encryption_pwsalt(struct file *filp, unsigned long arg)
 		goto out_err;
 	}
 got_it:
-	if (copy_to_user((__u8 __user *)arg, sbi->raw_super->encrypt_pw_salt,
-									16))
-		err = -EFAULT;
+	memcpy(encrypt_pw_salt, sbi->raw_super->encrypt_pw_salt, 16);
 out_err:
 	f2fs_up_write(&sbi->sb_lock);
 	mnt_drop_write_file(filp);
+
+	if (!err && copy_to_user((__u8 __user *)arg, encrypt_pw_salt, 16))
+		err = -EFAULT;
+
 	return err;
 }