[PATCH] fs/ntfs3: fix double ni_unlock() in ntfs_readdir()

[Christian Aurich Zanettini Martins]

Commit da4391c496fe ("ntfs3: release ni_lock before dir_emit in
ntfs_readdir to fix deadlocks") drops ni_lock before calling
ntfs_read_hdr() in ntfs_readdir(). If either call returns non-zero,
execution jumps to out, which calls ni_unlock() even though the lock
is no longer held.

This also happens when getdents64() fills the supplied buffer,
triggering a lockdep "bad unlock balance" warning.

Jump to out_free instead to avoid unlocking an already released lock.

Reported-by: syzbot+5c0ed4f2974a8b100ed4@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=5c0ed4f2974a8b100ed4
Fixes: da4391c496fe ("ntfs3: release ni_lock before dir_emit in ntfs_readdir to fix deadlocks")
Signed-off-by: Christian Aurich Zanettini Martins <christian.aurichzm@xxxxxxxxx>
---
Based on Paragon's ntfs3 master (da4391c496fe), also in linux-next.

Tested in QEMU with lockdep. A 128-byte getdents64() buffer
reproduced the warning before the fix. After the fix, no warning
occurred when reading root-only and 700-entry directories,
including four concurrent readers and a writer.

 fs/ntfs3/dir.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs3/dir.c b/fs/ntfs3/dir.c
index b54828735d55..45d6a41a7222 100644
--- a/fs/ntfs3/dir.c
+++ b/fs/ntfs3/dir.c
@@ -563,7 +563,7 @@ static int ntfs_readdir(struct file *file, struct dir_context *ctx)
 		 */
 		err = ntfs_read_hdr(sbi, ni, &root->ihdr, 0, pos, name, ctx);
 		if (err)
-			goto out;
+			goto out_free;

 		ni_lock(ni);
 		bit = 0;
@@ -607,7 +607,7 @@ static int ntfs_readdir(struct file *file, struct dir_context *ctx)
 				    ((u64)bit << index_bits) + sbi->record_size,
 				    pos, name, ctx);
 		if (err)
-			goto out;
+			goto out_free;

 		ni_lock(ni);
 	}
@@ -615,6 +615,7 @@ static int ntfs_readdir(struct file *file, struct dir_context *ctx)
 out:
 	ni_unlock(ni);

+out_free:
 	kfree(name);
 	put_indx_node(node);

base-commit: da4391c496fedc1ca78a99907712f2256ce8fb80