[PATCH 1/5] ocfs2: validate inline xattr header before ibody lookups

[ZhengYuan Huang <gality369@gmail.com>]

[BUG]
mknodat() can read past the end of a dinode block when ACL inheritance
walks a corrupted inode-body xattr header. Another report shows the same
unchecked lookup later faulting in the VFS open path after create
returns a garbage status.

KASAN: use-after-free in
ocfs2_xattr_find_entry+0x37b/0x3a0 fs/ocfs2/xattr.c:1078
Read of size 2 at addr ffff88801c520300 by task syz.0.10/360

Trace:
 ...
 ocfs2_xattr_find_entry+0x37b/0x3a0 fs/ocfs2/xattr.c:1078
 ocfs2_xattr_ibody_get fs/ocfs2/xattr.c:1178 [inline]
 ocfs2_xattr_get_nolock+0x2ee/0x1110 fs/ocfs2/xattr.c:1309
 ocfs2_calc_xattr_init+0x716/0xac0 fs/ocfs2/xattr.c:628
 ocfs2_mknod+0x935/0x2400 fs/ocfs2/namei.c:333
 ocfs2_create+0x158/0x390 fs/ocfs2/namei.c:676
 vfs_create fs/namei.c:3493 [inline]
 vfs_create+0x445/0x6f0 fs/namei.c:3477
 do_mknodat+0x2d8/0x5e0 fs/namei.c:4372
 __do_sys_mknodat fs/namei.c:4400 [inline]
 __se_sys_mknodat fs/namei.c:4397 [inline]
 __x64_sys_mknodat+0xb6/0xf0 fs/namei.c:4397
 ...

Another report:
 BUG: unable to handle page fault for address: fffffbfff3e40ec0
 RIP: 0010:__d_entry_type include/linux/dcache.h:414 [inline]
 RIP: 0010:d_can_lookup include/linux/dcache.h:429 [inline]
 RIP: 0010:d_is_dir include/linux/dcache.h:439 [inline]
 RIP: 0010:path_openat+0xe2f/0x2ce0 fs/namei.c:4134

Trace:
 ...
 do_filp_open+0x1f6/0x430 fs/namei.c:4161
 do_sys_openat2+0x117/0x1c0 fs/open.c:1437
 __x64_sys_openat+0x15b/0x220 fs/open.c:1463
 ...

[CAUSE]
ocfs2_xattr_ibody_list() already validates the inline xattr size and
entry count, but ocfs2_xattr_ibody_get() and ocfs2_xattr_ibody_find()
still derive the inline header directly from di->i_xattr_inline_size and
then trust xh_count. A corrupted inline size or entry count can therefore
move the computed header outside the dinode block before get/find start
walking it. That can either make ocfs2_xattr_find_entry() dereference
xs->header->xh_count outside the block or make ocfs2_xattr_get_nolock()
bubble a garbage status back through ocfs2_calc_xattr_init() into the
create/open path.

[FIX]
Factor the existing ibody header geometry checks into a shared helper.
Use it in ocfs2_xattr_ibody_get() and ocfs2_xattr_ibody_find(), and have
ocfs2_xattr_ibody_list() reuse the same helper instead of open-coding
the validation. Reject corrupt ibody metadata with -EFSCORRUPTED before
the lookup path can walk bogus xattr geometry or return a garbage status.

Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
---
 fs/ocfs2/xattr.c | 82 +++++++++++++++++++++++++++---------------------
 1 file changed, 47 insertions(+), 35 deletions(-)

diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
index 86cfd4c2adf9..3a5a17cdcf7e 100644
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@ -950,6 +950,41 @@ static int ocfs2_xattr_list_entries(struct inode *inode,
 	return result;
 }
 
+static int ocfs2_xattr_ibody_lookup_header(struct inode *inode,
+					   struct ocfs2_dinode *di,
+					   struct ocfs2_xattr_header **header)
+{
+	u16 xattr_count;
+	size_t max_entries;
+	u16 inline_size = le16_to_cpu(di->i_xattr_inline_size);
+
+	if (inline_size > inode->i_sb->s_blocksize ||
+	    inline_size < sizeof(struct ocfs2_xattr_header)) {
+		ocfs2_error(inode->i_sb,
+			    "Invalid xattr inline size %u in inode %llu\n",
+			    inline_size,
+			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
+		return -EFSCORRUPTED;
+	}
+
+	*header = (struct ocfs2_xattr_header *)
+		((void *)di + inode->i_sb->s_blocksize - inline_size);
+
+	xattr_count = le16_to_cpu((*header)->xh_count);
+	max_entries = (inline_size - sizeof(struct ocfs2_xattr_header)) /
+		      sizeof(struct ocfs2_xattr_entry);
+
+	if (xattr_count > max_entries) {
+		ocfs2_error(inode->i_sb,
+			    "xattr entry count %u exceeds maximum %zu in inode %llu\n",
+			    xattr_count, max_entries,
+			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
+		return -EFSCORRUPTED;
+	}
+
+	return 0;
+}
+
 int ocfs2_has_inline_xattr_value_outside(struct inode *inode,
 					 struct ocfs2_dinode *di)
 {
@@ -975,39 +1010,13 @@ static int ocfs2_xattr_ibody_list(struct inode *inode,
 	struct ocfs2_xattr_header *header = NULL;
 	struct ocfs2_inode_info *oi = OCFS2_I(inode);
 	int ret = 0;
-	u16 xattr_count;
-	size_t max_entries;
-	u16 inline_size;
 
 	if (!(oi->ip_dyn_features & OCFS2_INLINE_XATTR_FL))
 		return ret;
 
-	inline_size = le16_to_cpu(di->i_xattr_inline_size);
-
-	/* Validate inline size is reasonable */
-	if (inline_size > inode->i_sb->s_blocksize ||
-	    inline_size < sizeof(struct ocfs2_xattr_header)) {
-		ocfs2_error(inode->i_sb,
-			    "Invalid xattr inline size %u in inode %llu\n",
-			    inline_size,
-			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
-		return -EFSCORRUPTED;
-	}
-
-	header = (struct ocfs2_xattr_header *)
-		 ((void *)di + inode->i_sb->s_blocksize - inline_size);
-
-	xattr_count = le16_to_cpu(header->xh_count);
-	max_entries = (inline_size - sizeof(struct ocfs2_xattr_header)) /
-		       sizeof(struct ocfs2_xattr_entry);
-
-	if (xattr_count > max_entries) {
-		ocfs2_error(inode->i_sb,
-			    "xattr entry count %u exceeds maximum %zu in inode %llu\n",
-			    xattr_count, max_entries,
-			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
-		return -EFSCORRUPTED;
-	}
+	ret = ocfs2_xattr_ibody_lookup_header(inode, di, &header);
+	if (ret)
+		return ret;
 
 	ret = ocfs2_xattr_list_entries(inode, header, buffer, buffer_size);
 
@@ -1200,8 +1209,9 @@ static int ocfs2_xattr_ibody_get(struct inode *inode,
 		return -ENODATA;
 
 	xs->end = (void *)di + inode->i_sb->s_blocksize;
-	xs->header = (struct ocfs2_xattr_header *)
-			(xs->end - le16_to_cpu(di->i_xattr_inline_size));
+	ret = ocfs2_xattr_ibody_lookup_header(inode, di, &xs->header);
+	if (ret)
+		return ret;
 	xs->base = (void *)xs->header;
 	xs->here = xs->header->xh_entries;
 
@@ -2726,12 +2736,14 @@ static int ocfs2_xattr_ibody_find(struct inode *inode,
 
 	xs->xattr_bh = xs->inode_bh;
 	xs->end = (void *)di + inode->i_sb->s_blocksize;
-	if (oi->ip_dyn_features & OCFS2_INLINE_XATTR_FL)
-		xs->header = (struct ocfs2_xattr_header *)
-			(xs->end - le16_to_cpu(di->i_xattr_inline_size));
-	else
+	if (oi->ip_dyn_features & OCFS2_INLINE_XATTR_FL) {
+		ret = ocfs2_xattr_ibody_lookup_header(inode, di, &xs->header);
+		if (ret)
+			return ret;
+	} else {
 		xs->header = (struct ocfs2_xattr_header *)
 			(xs->end - OCFS2_SB(inode->i_sb)->s_xattr_inline_size);
+	}
 	xs->base = (void *)xs->header;
 	xs->here = xs->header->xh_entries;
 
-- 
2.43.0