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Sat, 27 Dec 2025 06:43:14 -0800 (PST) Received: from prometheus ([85.11.110.37]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-64b916b82e7sm27907219a12.35.2025.12.27.06.43.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 27 Dec 2025 06:43:13 -0800 (PST) From: Szymon Wilczek To: Konstantin Komarov Cc: ntfs3@lists.linux.dev, linux-kernel@vger.kernel.org, syzbot+d27edf9f96ae85939222@syzkaller.appspotmail.com, Szymon Wilczek Subject: [PATCH] ntfs3: fix circular locking dependency in run_unpack_ex Date: Sat, 27 Dec 2025 15:43:07 +0100 Message-ID: <20251227144307.8966-1-swilczek.lx@gmail.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Syzbot reported a circular locking dependency between wnd->rw_lock (sbi->used.bitmap) and ni->file.run_lock. The deadlock scenario: 1. ntfs_extend_mft() takes ni->file.run_lock then wnd->rw_lock. 2. run_unpack_ex() takes wnd->rw_lock then tries to acquire ni->file.run_lock inside ntfs_refresh_zone(). This creates an AB-BA deadlock. Fix this by using down_read_trylock() instead of down_read() when acquiring run_lock in run_unpack_ex(). If the lock is contended, skip ntfs_refresh_zone() - the MFT zone will be refreshed on the next MFT operation. This breaks the circular dependency since we never block waiting for run_lock while holding wnd->rw_lock. Reported-by: syzbot+d27edf9f96ae85939222@syzkaller.appspotmail.com Tested-by: syzbot+d27edf9f96ae85939222@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Dd27edf9f96ae85939222 Signed-off-by: Szymon Wilczek --- fs/ntfs3/run.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/fs/ntfs3/run.c b/fs/ntfs3/run.c index 395b20492525..dc59cad4fa37 100644 --- a/fs/ntfs3/run.c +++ b/fs/ntfs3/run.c @@ -1131,11 +1131,14 @@ int run_unpack_ex(struct runs_tree *run, struct ntf= s_sb_info *sbi, CLST ino, struct rw_semaphore *lock =3D is_mounted(sbi) ? &sbi->mft.ni->file.run_lock : NULL; - if (lock) - down_read(lock); - ntfs_refresh_zone(sbi); - if (lock) - up_read(lock); + if (lock) { + if (down_read_trylock(lock)) { + ntfs_refresh_zone(sbi); + up_read(lock); + } + } else { + ntfs_refresh_zone(sbi); + } } up_write(&wnd->rw_lock); if (err) --=20 2.52.0