linux-kernel - [PATCH] filelock: Fix fcntl/close race recovery compat path

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Message-Id: <20240723-fs-lock-recover-compatfix-v1-1-148096719529@google.com>
Date: Tue, 23 Jul 2024 17:03:56 +0200
From: Jann Horn <jannh@...gle.com>
To: Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 Jeff Layton <jlayton@...nel.org>, Chuck Lever <chuck.lever@...cle.com>, 
 Alexander Aring <alex.aring@...il.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
 stable@...nel.org, Jann Horn <jannh@...gle.com>
Subject: [PATCH] filelock: Fix fcntl/close race recovery compat path

When I wrote commit 3cad1bc01041 ("filelock: Remove locks reliably when
fcntl/close race is detected"), I missed that there are two copies of the
code I was patching: The normal version, and the version for 64-bit offsets
on 32-bit kernels.
Thanks to Greg KH for stumbling over this while doing the stable
backport...

Apply exactly the same fix to the compat path for 32-bit kernels.

Fixes: c293621bbf67 ("[PATCH] stale POSIX lock handling")
Cc: stable@...nel.org
Link: https://bugs.chromium.org/p/project-zero/issues/detail?id=2563
Signed-off-by: Jann Horn <jannh@...gle.com>
---
 fs/locks.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index bdd94c32256f..9afb16e0683f 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2570,8 +2570,9 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
 	error = do_lock_file_wait(filp, cmd, file_lock);
 
 	/*
-	 * Attempt to detect a close/fcntl race and recover by releasing the
-	 * lock that was just acquired. There is no need to do that when we're
+	 * Detect close/fcntl races and recover by zapping all POSIX locks
+	 * associated with this file and our files_struct, just like on
+	 * filp_flush(). There is no need to do that when we're
 	 * unlocking though, or for OFD locks.
 	 */
 	if (!error && file_lock->c.flc_type != F_UNLCK &&
@@ -2586,9 +2587,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
 		f = files_lookup_fd_locked(files, fd);
 		spin_unlock(&files->file_lock);
 		if (f != filp) {
-			file_lock->c.flc_type = F_UNLCK;
-			error = do_lock_file_wait(filp, cmd, file_lock);
-			WARN_ON_ONCE(error);
+			locks_remove_posix(filp, files);
 			error = -EBADF;
 		}
 	}

---
base-commit: 66ebbdfdeb093e097399b1883390079cd4c3022b
change-id: 20240723-fs-lock-recover-compatfix-cf2cbab343d1
-- 
Jann Horn <jannh@...gle.com>