From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Zhan Xusheng <zhanxusheng@xiaomi.com>,
	Konstantin Komarov <almaz.alexandrovich@paragon-software.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12 1127/1376] fs/ntfs3: reject out-of-range evcn in mi_enum_attr()
Date: Sat, 12 Sep 2026 08:59:13 +0200
Message-ID: <20260912065632.683752107@linuxfoundation.org>
In-Reply-To: <20260912065607.535295758@linuxfoundation.org>
References: <20260912065607.535295758@linuxfoundation.org>
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6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Zhan Xusheng <zhanxusheng1024@gmail.com>

[ Upstream commit 20fd9f64c0050658f2031e6bd5d552c6f0c8f7e3 ]

In mi_enum_attr(), the start/end VCN validation for non-resident
attributes is:

	if (svcn > evcn + 1) goto out;

When evcn is U64_MAX the "evcn + 1" expression wraps to 0 and any svcn
passes the check. For evcn values close to U64_MAX (but not equal to it)
the right-hand side is still a meaningless near-wrap upper bound, so a
malformed on-disk attribute with svcn == 0 and evcn near U64_MAX can pass
mi_enum_attr() unrejected.

VCN (virtual cluster number) is a cluster index, so any valid evcn is
bounded by the volume's total cluster count, which ntfs3 holds in
sbi->used.bitmap.nbits (set up in ntfs_init_from_boot() before any caller
of mi_enum_attr() runs). Reject evcn values that fall outside this range.

However, an empty non-resident attribute (no allocated clusters) is
legitimately encoded with svcn == 0 and evcn == -1 (U64_MAX), e.g. via
attr->nres.evcn = cpu_to_le64((u64)vcn - 1) with vcn == 0. That sentinel
must keep passing, so exclude evcn == U64_MAX from the range check. The
existing "svcn > evcn + 1" test still tolerates the sentinel ("0 > 0" is
false) and continues to require svcn == 0 for it, while the range check
rejects every other out-of-range evcn and thereby also defuses the
"evcn + 1" wraparound.

svcn does not need its own bound: once evcn < nbits, "svcn > evcn + 1"
implies svcn <= nbits.

Fixes: 013ff63b6494 ("fs/ntfs3: Add more attributes checks in mi_enum_attr()")
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
[almaz.alexandrovich@paragon-software.com: fixed evcn check]
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ntfs3/record.c | 34 +++++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/fs/ntfs3/record.c b/fs/ntfs3/record.c
index 714c7ecedca83..0f8ba76094fe1 100644
--- a/fs/ntfs3/record.c
+++ b/fs/ntfs3/record.c
@@ -202,7 +202,7 @@ struct ATTRIB *mi_enum_attr(struct ntfs_inode *ni, struct mft_inode *mi,
 	u32 used = le32_to_cpu(rec->used);
 	u32 t32, off, asize, prev_type;
 	u16 t16;
-	u64 data_size, alloc_size, tot_size;
+	u64 svcn, evcn, data_size, alloc_size, tot_size;
 
 	if (!attr) {
 		u32 total = le32_to_cpu(rec->total);
@@ -310,10 +310,38 @@ struct ATTRIB *mi_enum_attr(struct ntfs_inode *ni, struct mft_inode *mi,
 	if (t32 && le16_to_cpu(attr->name_off) + t32 > t16)
 		goto out;
 
-	/* Check start/end vcn. */
-	if (le64_to_cpu(attr->nres.svcn) > le64_to_cpu(attr->nres.evcn) + 1)
+	/*
+	 * Check start/end vcn.  svcn == 0 with evcn == -1 (U64_MAX) is the
+	 * sentinel for an empty non-resident attribute (no allocated
+	 * clusters) and must be accepted: "svcn > evcn + 1" tolerates it,
+	 * since "(u64)-1 + 1" is 0 and "0 > 0" is false.
+	 *
+	 * For a non-empty attribute evcn is a cluster index and must lie
+	 * within the volume (sbi->used.bitmap.nbits, set up in
+	 * ntfs_init_from_boot() before any caller of mi_enum_attr() runs).
+	 * Bounding evcn also prevents a malformed value close to U64_MAX
+	 * from slipping through the near-wrap "evcn + 1" upper bound.
+	 */
+	svcn = le64_to_cpu(attr->nres.svcn);
+	evcn = le64_to_cpu(attr->nres.evcn);
+	if (svcn > evcn + 1)
 		goto out;
 
+	if (is_attr_ext(attr)) {
+		/* sparsed/compressed attribute. */
+#ifdef CONFIG_NTFS3_64BIT_CLUSTER
+		/* No limits. */
+#else
+		/* Check evcn fits into 32 bits. */
+		if (evcn != U64_MAX && evcn >= (1ull << 32))
+			goto out;
+#endif
+	} else {
+		/* Check out of volume for normal attribute. */
+		if (evcn != U64_MAX && evcn >= mi->sbi->used.bitmap.nbits)
+			goto out;
+	}
+
 	data_size = le64_to_cpu(attr->nres.data_size);
 	if (le64_to_cpu(attr->nres.valid_size) > data_size)
 		goto out;
-- 
2.53.0