On 13.03.19 г. 10:55 ч., Qu Wenruo wrote:
> [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 <[email protected]>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202763
> Signed-off-by: Qu Wenruo <[email protected]>
Reviewed-by: Nikolay Borisov <[email protected]>
> ---
> 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;
>
