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([2405:201:682f:383f:4345:dc30:cb53:18e2]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-834ed6dd823sm331484b3a.38.2026.04.28.18.47.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Apr 2026 18:47:19 -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, stable@vger.kernel.org Subject: [PATCH v2] nilfs2: reject CLEAN_SEGMENTS ioctl with out-of-range segment numbers Date: Wed, 29 Apr 2026 07:17:11 +0530 Message-ID: <20260429014711.102110-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: stable@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") Cc: stable@vger.kernel.org Tested-by: syzbot+62f0f99d2f2bb8e3bbd7@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/20260428040256.84403-1-kartikey406@gmail.com/T/ [v1] Signed-off-by: Deepanshu Kartikey --- Changes in v2: - Reuse existing 'n' loop variable instead of introducing a new one (Slava Dubeyko) - Add dedicated out_free_segnums label so the validation-failure path falls through the existing cleanup ladder rather than duplicating kfree(kbufs[4]) inline (Slava Dubeyko) --- fs/nilfs2/ioctl.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c index e0a606643e87..41e47f558600 100644 --- a/fs/nilfs2/ioctl.c +++ b/fs/nilfs2/ioctl.c @@ -876,6 +876,20 @@ 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 (n = 0; n < nsegs; n++) { + if (((__u64 *)kbufs[4])[n] >= nilfs->ns_nsegments) { + ret = -EINVAL; + goto out_free_segnums; + } + } + for (n = 0; n < 4; n++) { ret = -EINVAL; if (argv[n].v_size != argsz[n]) @@ -928,6 +942,7 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp, out_free: while (--n >= 0) kvfree(kbufs[n]); +out_free_segnums: kfree(kbufs[4]); out: mnt_drop_write_file(filp); -- 2.43.0