[PATCH] fs/ntfs3: validate index entry key bounds

[ZhengYuan Huang <gality369@gmail.com>]

[BUG]
A malformed NTFS directory index entry can advertise a key_size larger
than the bytes actually present in its NTFS_DE payload. Directory lookup
then passes that malformed key to cmp_fnames(), which can read past the
end of the kmalloc'ed index buffer.

BUG: KASAN: slab-out-of-bounds in fname_full_size fs/ntfs3/ntfs.h:590 [inline]
BUG: KASAN: slab-out-of-bounds in cmp_fnames+0x1ea/0x230 fs/ntfs3/index.c:46
Read of size 1 at addr ffff88801c313018 by task syz.6.3365/9279

Call Trace:
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xbe/0x130 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xd1/0x650 mm/kasan/report.c:482
 kasan_report+0xfb/0x140 mm/kasan/report.c:595
 __asan_report_load1_noabort+0x14/0x30 mm/kasan/report_generic.c:378
 fname_full_size fs/ntfs3/ntfs.h:590 [inline]
 cmp_fnames+0x1ea/0x230 fs/ntfs3/index.c:46
 hdr_find_e.isra.0+0x3ed/0x670 fs/ntfs3/index.c:762
 indx_find+0x4b5/0x900 fs/ntfs3/index.c:1186
 dir_search_u+0x2c0/0x460 fs/ntfs3/dir.c:254
 ntfs_lookup+0x1cc/0x2a0 fs/ntfs3/namei.c:85
 __lookup_slow+0x241/0x450 fs/namei.c:1816
 lookup_slow fs/namei.c:1833 [inline]
 walk_component+0x31c/0x570 fs/namei.c:2151
 link_path_walk+0x592/0xd60 fs/namei.c:2519
 path_lookupat+0x138/0x660 fs/namei.c:2675
 filename_lookup+0x1f3/0x560 fs/namei.c:2705
 filename_setxattr+0xad/0x1c0 fs/xattr.c:660
 path_setxattrat+0x1d8/0x280 fs/xattr.c:713
 __do_sys_lsetxattr fs/xattr.c:754 [inline]
 __se_sys_lsetxattr fs/xattr.c:750 [inline]
 __x64_sys_lsetxattr+0xd0/0x150 fs/xattr.c:750
 ...

Allocated by task 9279:
 kasan_save_stack+0x39/0x70 mm/kasan/common.c:56
 kasan_save_track+0x14/0x40 mm/kasan/common.c:77
 kasan_save_alloc_info+0x37/0x60 mm/kasan/generic.c:573
 poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
 __kasan_kmalloc+0xc3/0xd0 mm/kasan/common.c:417
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5650 [inline]
 __kmalloc_noprof+0x2bd/0x900 mm/slub.c:5662
 kmalloc_noprof include/linux/slab.h:961 [inline]
 indx_read+0x41d/0xad0 fs/ntfs3/index.c:1059
 indx_find+0x447/0x900 fs/ntfs3/index.c:1179
 dir_search_u+0x2c0/0x460 fs/ntfs3/dir.c:254
 ntfs_lookup+0x1cc/0x2a0 fs/ntfs3/namei.c:85
 __lookup_slow+0x241/0x450 fs/namei.c:1816
 lookup_slow fs/namei.c:1833 [inline]
 walk_component+0x31c/0x570 fs/namei.c:2151
 link_path_walk+0x592/0xd60 fs/namei.c:2519
 path_lookupat+0x138/0x660 fs/namei.c:2675
 filename_lookup+0x1f3/0x560 fs/namei.c:2705
 filename_setxattr+0xad/0x1c0 fs/xattr.c:660
 path_setxattrat+0x1d8/0x280 fs/xattr.c:713
 __do_sys_lsetxattr fs/xattr.c:754 [inline]
 __se_sys_lsetxattr fs/xattr.c:750 [inline]
 __x64_sys_lsetxattr+0xd0/0x150 fs/xattr.c:750
 ...

[CAUSE]
The index-header validators only validated INDEX_HDR-level geometry.
They did not walk each NTFS_DE to verify entry alignment, subnode
layout, or that key_size fit inside the entry payload. They also
allowed a last sentinel entry to carry a non-zero key_size.

[FIX]
Walk every NTFS_DE in ntfs3's index-header validators and reject
entries with invalid layout, mismatched subnode state, oversized
key_size, or non-zero sentinel keys before lookup or log replay can
consume them.

Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
---
fs/ntfs3/fslog.c | 26 ++++++++++++++++++++------
fs/ntfs3/index.c | 37 ++++++++++++++++++++++++++++++++++++-
2 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/fs/ntfs3/fslog.c b/fs/ntfs3/fslog.c
index acfa18b84401..ff8e2a808d12 100644
--- a/fs/ntfs3/fslog.c
+++ b/fs/ntfs3/fslog.c
@@ -2599,11 +2599,12 @@ static int read_next_log_rec(struct ntfs_log *log, struct lcb *lcb, u64 *lsn)
 
 bool check_index_header(const struct INDEX_HDR *hdr, size_t bytes)
 {
+	const bool has_subnode = hdr_has_subnode(hdr);
 	__le16 mask;
 	u32 min_de, de_off, used, total;
 	const struct NTFS_DE *e;
 
-	if (hdr_has_subnode(hdr)) {
+	if (has_subnode) {
 		min_de = sizeof(struct NTFS_DE) + sizeof(u64);
 		mask = NTFS_IE_HAS_SUBNODES;
 	} else {
@@ -2620,20 +2621,33 @@ bool check_index_header(const struct INDEX_HDR *hdr, size_t bytes)
 		return false;
 	}
 
-	e = Add2Ptr(hdr, de_off);
+	e = (const struct NTFS_DE *)((const u8 *)hdr + de_off);
 	for (;;) {
 		u16 esize = le16_to_cpu(e->size);
-		struct NTFS_DE *next = Add2Ptr(e, esize);
+		u16 key_size = le16_to_cpu(e->key_size);
+		u16 data_size;
 
-		if (esize < min_de || PtrOffset(hdr, next) > used ||
+		if (!IS_ALIGNED(esize, 8) || esize < min_de ||
 		    (e->flags & NTFS_IE_HAS_SUBNODES) != mask) {
 			return false;
 		}
 
-		if (de_is_last(e))
+		if (size_add(de_off, esize) > used)
+			return false;
+
+		if (de_is_last(e)) {
+			if (key_size)
+				return false;
+
 			break;
+		}
+
+		data_size = esize - min_de;
+		if (key_size > data_size)
+			return false;
 
-		e = next;
+		de_off += esize;
+		e = (const struct NTFS_DE *)((const u8 *)hdr + de_off);
 	}
 
 	return true;
diff --git a/fs/ntfs3/index.c b/fs/ntfs3/index.c
index 5344b29b0577..faedfadf6335 100644
--- a/fs/ntfs3/index.c
+++ b/fs/ntfs3/index.c
@@ -611,16 +611,51 @@ static const struct NTFS_DE *hdr_insert_head(struct INDEX_HDR *hdr,
  */
 static bool index_hdr_check(const struct INDEX_HDR *hdr, u32 bytes)
 {
+	const bool has_subnode = hdr_has_subnode(hdr);
+	const u16 min_size = sizeof(struct NTFS_DE) +
+			     (has_subnode ? sizeof(u64) : 0);
 	u32 end = le32_to_cpu(hdr->used);
 	u32 tot = le32_to_cpu(hdr->total);
 	u32 off = le32_to_cpu(hdr->de_off);
+	const struct NTFS_DE *e;
 
 	if (!IS_ALIGNED(off, 8) || tot > bytes || end > tot ||
-	    size_add(off, sizeof(struct NTFS_DE)) > end) {
+	    size_add(off, min_size) > end) {
 		/* incorrect index buffer. */
 		return false;
 	}
 
+	/* Ensure every key stays inside its entry before lookup walks it. */
+	e = (const struct NTFS_DE *)((const u8 *)hdr + off);
+	for (;;) {
+		u16 e_size = le16_to_cpu(e->size);
+		u16 key_size = le16_to_cpu(e->key_size);
+		u16 data_size;
+
+		if (!IS_ALIGNED(e_size, 8) || e_size < min_size ||
+		    de_has_vcn(e) != has_subnode) {
+			/* incorrect index entry. */
+			return false;
+		}
+
+		if (size_add(off, e_size) > end)
+			return false;
+
+		if (de_is_last(e)) {
+			if (key_size)
+				return false;
+
+			break;
+		}
+
+		data_size = e_size - min_size;
+		if (key_size > data_size)
+			return false;
+
+		off += e_size;
+		e = (const struct NTFS_DE *)((const u8 *)hdr + off);
+	}
+
 	return true;
 }