[SRU Bionic PATCH 1/2] ext4: check if directory block is within i_size

[Cengiz Can]

From: Lukas Czerner <lczerner at redhat.com>

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 at redhat.com>
Cc: stable at vger.kernel.org
Reviewed-by: Andreas Dilger <adilger at dilger.ca>
Link: https://lore.kernel.org/r/20220704142721.157985-1-lczerner@redhat.com
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
CVE-2022-1184
(backported from commit 65f8ea4cd57dbd46ea13b41dc8bac03176b04233)
[cengizcan: adjust context because we don't have commit 46f870d690fe ("ext4:
simulate various I/O and checksum errors when reading metadata") in tree.]
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 fs/ext4/namei.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index c71a1533404a..f8faf6d742cd 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -123,6 +123,13 @@ 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);
+	}
+
 	bh = ext4_bread(NULL, inode, block, 0);
 	if (IS_ERR(bh)) {
 		__ext4_warning(inode->i_sb, func, line,
-- 
2.39.2