ext4: check if directory block is within i_size

Currently ext4 directory handling code implicitly assumes that the
directory blocks are always within the i_size. In fact ext4_append()
will attempt to allocate next directory block based solely on i_size and
the i_size is then appropriately increased after a successful
allocation.

However, for this to work it requires i_size to be correct. If, for any
reason, the directory inode i_size is corrupted in a way that the
directory tree refers to a valid directory block past i_size, we could
end up corrupting parts of the directory tree structure by overwriting
already used directory blocks when modifying the directory.

Fix it by catching the corruption early in __ext4_read_dirblock().

Addresses Red-Hat-Bugzilla: #2070205
CVE: CVE-2022-1184
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Cc: stable@vger.kernel.org
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20220704142721.157985-1-lczerner@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 1c6725e..7fced54 100644 (file)
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -110,6 +110,13 @@ static struct buffer_head *__ext4_read_dirblock(struct inode *inode,
        struct ext4_dir_entry *dirent;
        int is_dx_block = 0;
 
+       if (block >= inode->i_size) {
+               ext4_error_inode(inode, func, line, block,
+                      "Attempting to read directory block (%u) that is past i_size (%llu)",
+                      block, inode->i_size);
+               return ERR_PTR(-EFSCORRUPTED);
+       }
+
        if (ext4_simulate_fail(inode->i_sb, EXT4_SIM_DIRBLOCK_EIO))
                bh = ERR_PTR(-EIO);
        else