From: Chao Yu <chao@kernel.org>

[ Upstream commit 8fc6056dcf79937c46c97fa4996cda65956437a9 ]

As reported, on-disk footer.ino and footer.nid is the same and
out-of-range, let's add sanity check on f2fs_alloc_nid() to detect
any potential corruption in free_nid_list.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Robert Garcia <rob_garcia@163.com>
---
 fs/f2fs/node.c          | 17 ++++++++++++++++-
 include/linux/f2fs_fs.h |  1 +
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 2555787c79bb..06c94680ae4e 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -27,12 +27,17 @@ static struct kmem_cache *free_nid_slab;
 static struct kmem_cache *nat_entry_set_slab;
 static struct kmem_cache *fsync_node_entry_slab;
 
+static inline bool is_invalid_nid(struct f2fs_sb_info *sbi, nid_t nid)
+{
+	return nid < F2FS_ROOT_INO(sbi) || nid >= NM_I(sbi)->max_nid;
+}
+
 /*
  * Check whether the given nid is within node id range.
  */
 int f2fs_check_nid_range(struct f2fs_sb_info *sbi, nid_t nid)
 {
-	if (unlikely(nid < F2FS_ROOT_INO(sbi) || nid >= NM_I(sbi)->max_nid)) {
+	if (unlikely(is_invalid_nid(sbi, nid))) {
 		set_sbi_flag(sbi, SBI_NEED_FSCK);
 		f2fs_warn(sbi, "%s: out-of-range nid=%x, run fsck to fix.",
 			  __func__, nid);
@@ -2593,6 +2598,16 @@ bool f2fs_alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
 		f2fs_bug_on(sbi, list_empty(&nm_i->free_nid_list));
 		i = list_first_entry(&nm_i->free_nid_list,
 					struct free_nid, list);
+
+		if (unlikely(is_invalid_nid(sbi, i->nid))) {
+			spin_unlock(&nm_i->nid_list_lock);
+			f2fs_err(sbi, "Corrupted nid %u in free_nid_list",
+								i->nid);
+			f2fs_stop_checkpoint(sbi, false,
+					STOP_CP_REASON_CORRUPTED_NID);
+			return false;
+		}
+
 		*nid = i->nid;
 
 		__move_free_nid(sbi, i, FREE_NID, PREALLOC_NID);
diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
index c61d8fc1deb3..26c7daca9959 100644
--- a/include/linux/f2fs_fs.h
+++ b/include/linux/f2fs_fs.h
@@ -81,6 +81,7 @@ enum stop_cp_reason {
 	STOP_CP_REASON_CORRUPTED_SUMMARY,
 	STOP_CP_REASON_UPDATE_INODE,
 	STOP_CP_REASON_FLUSH_FAIL,
+	STOP_CP_REASON_CORRUPTED_NID,
 	STOP_CP_REASON_MAX,
 };
 
-- 
2.34.1

On Thu, Apr 30, 2026 at 01:55:37PM +0800, Robert Garcia wrote:
> From: Chao Yu <chao@kernel.org>
>
> [ Upstream commit 8fc6056dcf79937c46c97fa4996cda65956437a9 ]
>
> As reported, on-disk footer.ino and footer.nid is the same and
> out-of-range, let's add sanity check on f2fs_alloc_nid() to detect
> any potential corruption in free_nid_list.

Thanks, queued for 6.1.y.

--
Thanks,
Sasha