[PATCH 6/6] btrfs: inode: Verify inode mode to avoid NULL pointer dereference

[Qu Wenruo <wqu@suse.com>]

[BUG]
When access a file on a crafted image, btrfs can crash in block layer:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
PGD 136501067 P4D 136501067 PUD 124519067 PMD 0
CPU: 3 PID: 0 Comm: swapper/3 Not tainted 5.0.0-rc8-default #252
RIP: 0010:end_bio_extent_readpage+0x144/0x700
Call Trace:
 <IRQ>
 blk_update_request+0x8f/0x350
 blk_mq_end_request+0x1a/0x120
 blk_done_softirq+0x99/0xc0
 __do_softirq+0xc7/0x467
 irq_exit+0xd1/0xe0
 call_function_single_interrupt+0xf/0x20
 </IRQ>
RIP: 0010:default_idle+0x1e/0x170

[CAUSE]
The crafted image has a pretty tricky corruption, the INODE_ITEM has a
different type against its parent dir:
        item 20 key (268 INODE_ITEM 0) itemoff 2808 itemsize 160
                generation 13 transid 13 size 1048576 nbytes 1048576
                block group 0 mode 121644 links 1 uid 0 gid 0 rdev 0
                sequence 9 flags 0x0(none)

This mode number 0120000 means it's a soft link.

But the dir item think it's still a regular file:
        item 8 key (264 DIR_INDEX 5) itemoff 3707 itemsize 32
                location key (268 INODE_ITEM 0) type FILE
                transid 13 data_len 0 name_len 2
                name: f4
        item 40 key (264 DIR_ITEM 51821248) itemoff 1573 itemsize 32
                location key (268 INODE_ITEM 0) type FILE
                transid 13 data_len 0 name_len 2
                name: f4

For btrfs symlink, we don't set BTRFS_I(inode)->io_tree.ops and leave
it empty, as symlink is only designed to have inlined extent, all
handled by tree block read.
Thus no need to trigger btrfs_submit_bio_hook() for inline file extent.

However for end_bio_extent_readpage() it expects tree->ops populated, as
it's reading regular data extent.
This causes NULL pointer dereference.

[FIX]
This patch fixes the problem by 2 directions:
- Verify inode mode against its dir item when looking up inode
  So in btrfs_lookup_dentry() if we find inode mode mismatch with dir
  item, we error out so that corrupted inode will not be access.

- Verify inode mode when getting extent mapping
  Only regular file should have regular or preallocated extent.
  If we found regular/preallocated file extent for soft link or
  whatever, we error out before we submit read bio.

With this fix that crafted image can be rejected gracefully:
  BTRFS critical (device loop0): inode mode mismatch with dir: inode mode=0121644 btrfs type=7 dir type=1

Reported-by: Yoon Jungyeon <jungyeon@gatech.edu>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=202763
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c             | 38 ++++++++++++++++++++++++++++--------
 fs/btrfs/tests/inode-tests.c |  1 +
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 5c349667c761..4ced641aaa8e 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5396,12 +5396,13 @@ void btrfs_evict_inode(struct inode *inode)
 }
 
 /*
- * this returns the key found in the dir entry in the location pointer.
+ * this returns the key found in the dir entry in the location pointer,
+ * fill @type with BTRFS_FT_*, and return 0.
  * If no dir entries were found, returns -ENOENT.
  * If found a corrupted location in dir entry, returns -EUCLEAN.
  */
 static int btrfs_inode_by_name(struct inode *dir, struct dentry *dentry,
-			       struct btrfs_key *location)
+			       struct btrfs_key *location, u8 *type)
 {
 	const char *name = dentry->d_name.name;
 	int namelen = dentry->d_name.len;
@@ -5430,6 +5431,8 @@ static int btrfs_inode_by_name(struct inode *dir, struct dentry *dentry,
 			   __func__, name, btrfs_ino(BTRFS_I(dir)),
 			   location->objectid, location->type, location->offset);
 	}
+	if (!ret)
+		*type = btrfs_dir_type(path->nodes[0], di);
 out:
 	btrfs_free_path(path);
 	return ret;
@@ -5667,6 +5670,11 @@ static struct inode *new_simple_dir(struct super_block *s,
 	return inode;
 }
 
+static inline u8 btrfs_inode_type(struct inode *inode)
+{
+	return btrfs_type_by_mode[(inode->i_mode & S_IFMT) >> S_SHIFT];
+}
+
 struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(dir->i_sb);
@@ -5674,18 +5682,29 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 	struct btrfs_root *root = BTRFS_I(dir)->root;
 	struct btrfs_root *sub_root = root;
 	struct btrfs_key location;
+	u8 di_type = 0;
 	int index;
 	int ret = 0;
 
 	if (dentry->d_name.len > BTRFS_NAME_LEN)
 		return ERR_PTR(-ENAMETOOLONG);
 
-	ret = btrfs_inode_by_name(dir, dentry, &location);
+	ret = btrfs_inode_by_name(dir, dentry, &location, &di_type);
 	if (ret < 0)
 		return ERR_PTR(ret);
 
 	if (location.type == BTRFS_INODE_ITEM_KEY) {
 		inode = btrfs_iget(dir->i_sb, &location, root, NULL);
+
+		/* Do extra check against inode mode with di_type */
+		if (btrfs_inode_type(inode) != di_type) {
+			btrfs_crit(fs_info,
+"inode mode mismatch with dir: inode mode=0%o btrfs type=%u dir type=%u",
+				  inode->i_mode, btrfs_inode_type(inode),
+				  di_type);
+			iput(inode);
+			return ERR_PTR(-EUCLEAN);
+		}
 		return inode;
 	}
 
@@ -6290,11 +6309,6 @@ static struct inode *btrfs_new_inode(struct btrfs_trans_handle *trans,
 	return ERR_PTR(ret);
 }
 
-static inline u8 btrfs_inode_type(struct inode *inode)
-{
-	return btrfs_type_by_mode[(inode->i_mode & S_IFMT) >> S_SHIFT];
-}
-
 /*
  * utility function to add 'inode' into 'parent_inode' with
  * a give name and a given sequence number.
@@ -6816,6 +6830,14 @@ struct extent_map *btrfs_get_extent(struct btrfs_inode *inode,
 	extent_start = found_key.offset;
 	if (found_type == BTRFS_FILE_EXTENT_REG ||
 	    found_type == BTRFS_FILE_EXTENT_PREALLOC) {
+		/* Only regular file could have regular/prealloc extent */
+		if (!S_ISREG(inode->vfs_inode.i_mode)) {
+			ret = -EUCLEAN;
+			btrfs_crit(fs_info,
+		"regular/prealloc extent found for non-regular inode %llu",
+				   btrfs_ino(inode));
+			goto out;
+		}
 		extent_end = extent_start +
 		       btrfs_file_extent_num_bytes(leaf, item);
 
diff --git a/fs/btrfs/tests/inode-tests.c b/fs/btrfs/tests/inode-tests.c
index af0c8e30d9e2..b01dbcab9eed 100644
--- a/fs/btrfs/tests/inode-tests.c
+++ b/fs/btrfs/tests/inode-tests.c
@@ -232,6 +232,7 @@ static noinline int test_btrfs_get_extent(u32 sectorsize, u32 nodesize)
 		return ret;
 	}
 
+	inode->i_mode = S_IFREG;
 	BTRFS_I(inode)->location.type = BTRFS_INODE_ITEM_KEY;
 	BTRFS_I(inode)->location.objectid = BTRFS_FIRST_FREE_OBJECTID;
 	BTRFS_I(inode)->location.offset = 0;
-- 
2.21.0