[PATCH v3 3/4] ext4: add EXT4_IGET_BAD flag to prevent unexpected bad inode

Baokun Li
2022-10-26T04:01:29Z

There are many places that will get unhappy (and crash) when ext4_iget()
returns a bad inode. However, if iget the boot loader inode, allows a bad
inode to be returned, because the inode may not be initialized. This
mechanism can be used to bypass some checks and cause panic. To solve this
problem, we add a special iget flag EXT4_IGET_BAD. Only with this flag
we'd be returning bad inode from ext4_iget(), otherwise we always return
the error code if the inode is bad inode.(suggested by Jan Kara)

Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
fs/ext4/ext4.h | 3 ++-
fs/ext4/inode.c | 8 +++++++-
fs/ext4/ioctl.c | 3 ++-
3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8d5453852f98..2b574b143bde 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2964,7 +2964,8 @@ int do_journal_get_write_access(handle_t *handle, struct inode *inode,
typedef enum {
EXT4_IGET_NORMAL = 0,
EXT4_IGET_SPECIAL = 0x0001, /* OK to iget a system inode */
- EXT4_IGET_HANDLE = 0x0002 /* Inode # is from a handle */
+ EXT4_IGET_HANDLE = 0x0002, /* Inode # is from a handle */
+ EXT4_IGET_BAD = 0x0004 /* Allow to iget a bad inode */
} ext4_iget_flags;

extern struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ae3a836dd9d7..f767340229fd 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5043,8 +5043,14 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
if (IS_CASEFOLDED(inode) && !ext4_has_feature_casefold(inode->i_sb))
ext4_error_inode(inode, function, line, 0,
"casefold flag without casefold feature");
- brelse(iloc.bh);
+ if (is_bad_inode(inode) && !(flags & EXT4_IGET_BAD)) {
+ ext4_error_inode(inode, function, line, 0,
+ "bad inode without EXT4_IGET_BAD flag");
+ ret = -EUCLEAN;
+ goto bad_inode;
+ }

+ brelse(iloc.bh);
unlock_new_inode(inode);
return inode;

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index ded535535b27..e0be8026c996 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -375,7 +375,8 @@ static long swap_inode_boot_loader(struct super_block *sb,
blkcnt_t blocks;
unsigned short bytes;

- inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO, EXT4_IGET_SPECIAL);
+ inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO,
+ EXT4_IGET_SPECIAL | EXT4_IGET_BAD);
if (IS_ERR(inode_bl))
return PTR_ERR(inode_bl);
ei_bl = EXT4_I(inode_bl);
--
2.31.1