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([2405:201:682f:383f:e9bf:615b:4859:6e22]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-834ed5cf7d4sm4353894b3a.23.2026.04.29.21.07.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Apr 2026 21:07:10 -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 v3] nilfs2: reject CLEAN_SEGMENTS ioctl with out-of-range segment numbers Date: Thu, 30 Apr 2026 09:37:04 +0530 Message-ID: <20260430040704.113622-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-nilfs@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 user-supplied segment numbers are not validated before nilfs_clean_segments() begins doing work; 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 holding 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 nilfs_clean_segments() immediately after acquiring ns_segctor_sem via nilfs_transaction_lock(). Holding ns_segctor_sem serializes the check against nilfs_ioctl_resize(), which can modify ns_nsegments, so the validation uses a consistent value. Out-of-range segment numbers are rejected with -EINVAL before any segment-cleaning work begins, so the bad entries never reach the per-element diagnostic path inside nilfs_sufile_updatev(). Reported-by: syzbot+62f0f99d2f2bb8e3bbd7@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=62f0f99d2f2bb8e3bbd7 Tested-by: syzbot+62f0f99d2f2bb8e3bbd7@syzkaller.appspotmail.com Fixes: 4f6b828837b4 ("nilfs2: fix lock order reversal in nilfs_clean_segments ioctl") Cc: stable@vger.kernel.org Signed-off-by: Deepanshu Kartikey --- Changes in v3: - Move validation from nilfs_ioctl_clean_segments() into nilfs_clean_segments(), under ns_segctor_sem held for write by nilfs_transaction_lock(), to serialize against nilfs_ioctl_resize() which can modify ns_nsegments (Ryusuke Konishi) - Introduce local variables segnumv and nfreesegs for readability, rather than open-coding casts of kbufs[4] (Ryusuke Konishi) - Emit nilfs_err() once on the first out-of-range segnum and bail out, instead of nilfs_warn() per element (Ryusuke Konishi) - Add bail_unlock label for the early-failure path, parallel to the existing out_unlock structure (Ryusuke Konishi) 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/segment.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c index 1491a4d4b1e1..dc54643866ce 100644 --- a/fs/nilfs2/segment.c +++ b/fs/nilfs2/segment.c @@ -2512,12 +2512,33 @@ int nilfs_clean_segments(struct super_block *sb, struct nilfs_argv *argv, struct nilfs_sc_info *sci = nilfs->ns_writer; struct nilfs_transaction_info ti; int err; + size_t i, nfreesegs = argv[4].v_nmembs; + __u64 *segnumv = kbufs[4]; if (unlikely(!sci)) return -EROFS; nilfs_transaction_lock(sb, &ti, 1); + /* + * Validate segment numbers under ns_segctor_sem (held for write + * by nilfs_transaction_lock above) so the check is serialized + * against nilfs_ioctl_resize(), which can modify ns_nsegments. + * Rejecting bad input here, before any segment-cleaning work + * begins, avoids the per-element diagnostic path inside + * nilfs_sufile_updatev() that would otherwise run under this + * same lock and stall concurrent readers. + */ + for (i = 0; i < nfreesegs; i++) { + if (segnumv[i] >= nilfs->ns_nsegments) { + nilfs_err(sb, + "Segment number %llu to be freed is out of range", + (unsigned long long)segnumv[i]); + err = -EINVAL; + goto bail_unlock; + } + } + err = nilfs_mdt_save_to_shadow_map(nilfs->ns_dat); if (unlikely(err)) goto out_unlock; @@ -2558,6 +2579,7 @@ int nilfs_clean_segments(struct super_block *sb, struct nilfs_argv *argv, sci->sc_freesegs = NULL; sci->sc_nfreesegs = 0; nilfs_mdt_clear_shadow_map(nilfs->ns_dat); + bail_unlock: nilfs_transaction_unlock(sb); return err; } -- 2.43.0