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([2405:201:682f:383f:3532:7d40:72e8:bc68]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c7fc6015691sm693675a12.18.2026.04.27.21.03.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Apr 2026 21:03:02 -0700 (PDT) From: Deepanshu Kartikey To: konishi.ryusuke@gmail.com, slava@dubeyko.com Cc: linux-nilfs@vger.kernel.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+62f0f99d2f2bb8e3bbd7@syzkaller.appspotmail.com Subject: [PATCH] nilfs2: reject CLEAN_SEGMENTS ioctl with out-of-range segment numbers Date: Tue, 28 Apr 2026 09:32:55 +0530 Message-ID: <20260428040256.84403-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Syzbot reported a hung task in nilfs_transaction_begin() where multiple tasks performing chmod() on a nilfs2 mount blocked for over 143 seconds waiting to acquire ns_segctor_sem for read: INFO: task syz.0.17:5918 blocked for more than 143 seconds. Call Trace: schedule+0x164/0x360 rwsem_down_read_slowpath+0x6d9/0x940 down_read+0x99/0x2e0 nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221 nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921 notify_change+0xc1a/0xf40 chmod_common+0x273/0x4a0 do_fchmodat+0x12d/0x230 The writer holding ns_segctor_sem was a concurrent NILFS_IOCTL_CLEAN_SEGMENTS caller, stuck inside printk while emitting per-element warnings from nilfs_sufile_updatev(): __nilfs_msg+0x373/0x450 fs/nilfs2/super.c:78 nilfs_sufile_updatev+0x21c/0x6d0 fs/nilfs2/sufile.c:186 nilfs_sufile_freev fs/nilfs2/sufile.h:93 [inline] nilfs_free_segments fs/nilfs2/segment.c:1140 [inline] nilfs_segctor_collect_blocks fs/nilfs2/segment.c:1261 [inline] nilfs_segctor_do_construct+0x1f55/0x76c0 nilfs_clean_segments+0x3bd/0xa50 nilfs_ioctl_clean_segments fs/nilfs2/ioctl.c:922 [inline] nilfs_ioctl+0x261f/0x2780 The root cause is that nilfs_ioctl_clean_segments() does not validate the user-supplied segment numbers in kbufs[4] before calling nilfs_clean_segments(), which acquires ns_segctor_sem for write. The range check on each segnum is performed deep inside the call chain by nilfs_sufile_updatev(), which emits a nilfs_warn() per invalid entry while still under the segctor lock and the sufile mi_sem. Under load (repeated invocations across multiple mounts saturating the global printk path), the cumulative printk latency keeps ns_segctor_sem held long enough to trip the hung_task watchdog, blocking concurrent operations such as chmod() that need ns_segctor_sem for read. Fix by validating the contents of kbufs[4] in the ioctl entry path, before any FS-wide lock is acquired. Out-of-range segment numbers are rejected with -EINVAL synchronously, with no work performed under ns_segctor_sem. Reported-by: syzbot+62f0f99d2f2bb8e3bbd7@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=62f0f99d2f2bb8e3bbd7 Fixes: 4f6b828837b4 ("nilfs2: fix lock order reversal in nilfs_clean_segments ioctl") Tested-by: syzbot+62f0f99d2f2bb8e3bbd7@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey --- fs/nilfs2/ioctl.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c index e0a606643e87..38822dce1839 100644 --- a/fs/nilfs2/ioctl.c +++ b/fs/nilfs2/ioctl.c @@ -846,6 +846,7 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp, struct the_nilfs *nilfs; size_t len, nsegs; int n, ret; + size_t i; if (!capable(CAP_SYS_ADMIN)) return -EPERM; @@ -876,6 +877,21 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp, } nilfs = inode->i_sb->s_fs_info; + /* + * Validate segment numbers against the filesystem's segment count + * before entering nilfs_clean_segments(), which acquires + * ns_segctor_sem for write. Catching invalid segnums here avoids + * holding that lock while emitting per-element diagnostics under + * the segment constructor. + */ + for (i = 0; i < nsegs; i++) { + if (((__u64 *)kbufs[4])[i] >= nilfs->ns_nsegments) { + ret = -EINVAL; + kfree(kbufs[4]); + goto out; + } + } + for (n = 0; n < 4; n++) { ret = -EINVAL; if (argv[n].v_size != argsz[n]) -- 2.43.0