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Subject[PATCH 4.9 06/42] btrfs: inode: Verify inode mode to avoid NULL pointer dereference
Date
From: Qu Wenruo <wqu@suse.com>

commit 6bf9e4bd6a277840d3fe8c5d5d530a1fbd3db592 upstream

[BUG]
When accessing 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 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 symlink.

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

[FIX]
This patch fixes the problem in two ways:

- 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 accessed.

- Verify inode mode when getting extent mapping
Only regular file should have regular or preallocated extent.
If we found regular/preallocated file extent for symlink or
the rest, we error out before submitting the 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
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[sudip: use original btrfs_inode_type(), btrfs_crit with root->fs_info,
ISREG with inode->i_mode and adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/btrfs/inode.c | 41 +++++++++++++++++++++++++++++++++--------
fs/btrfs/tests/inode-tests.c | 1 +
2 files changed, 34 insertions(+), 8 deletions(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5440,11 +5440,13 @@ no_delete:
}

/*
- * this returns the key found in the dir entry in the location pointer.
+ * Return 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, location->objectid is 0.
*/
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;
@@ -5466,6 +5468,8 @@ static int btrfs_inode_by_name(struct in
goto out_err;

btrfs_dir_item_key_to_cpu(path->nodes[0], di, location);
+ if (!ret)
+ *type = btrfs_dir_type(path->nodes[0], di);
out:
btrfs_free_path(path);
return ret;
@@ -5755,19 +5759,25 @@ static struct inode *new_simple_dir(stru
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 inode *inode;
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);

@@ -5776,6 +5786,18 @@ struct inode *btrfs_lookup_dentry(struct

if (location.type == BTRFS_INODE_ITEM_KEY) {
inode = btrfs_iget(dir->i_sb, &location, root, NULL);
+ if (IS_ERR(inode))
+ return inode;
+
+ /* Do extra check against inode mode with di_type */
+ if (btrfs_inode_type(inode) != di_type) {
+ btrfs_crit(root->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;
}

@@ -6391,11 +6413,6 @@ fail:
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.
@@ -6981,6 +6998,14 @@ again:
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->i_mode)) {
+ ret = -EUCLEAN;
+ btrfs_crit(root->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);
} else if (found_type == BTRFS_FILE_EXTENT_INLINE) {
--- a/fs/btrfs/tests/inode-tests.c
+++ b/fs/btrfs/tests/inode-tests.c
@@ -245,6 +245,7 @@ static noinline int test_btrfs_get_exten
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;

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