[PATCH 3.16 169/328] ext4: avoid divide by zero fault when deleting corrupted inline directories

Ben Hutchings
2018-12-09T22:24:20Z

From: Theodore Ts'o <tytso@mit.edu>

commit 4d982e25d0bdc83d8c64e66fdeca0b89240b3b85 upstream.

A specially crafted file system can trick empty_inline_dir() into
reading past the last valid entry in a inline directory, and then run
into the end of xattr marker. This will trigger a divide by zero
fault. Fix this by using the size of the inline directory instead of
dir->i_size.

Also clean up error reporting in __ext4_check_dir_entry so that the
message is clearer and more understandable --- and avoids the division
by zero trap if the size passed in is zero. (I'm not sure why we
coded it that way in the first place; printing offset % size is
actually more confusing and less useful.)

https://bugzilla.kernel.org/show_bug.cgi?id=200933

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/dir.c | 20 +++++++++-----------
fs/ext4/inline.c | 4 +++-
2 files changed, 12 insertions(+), 12 deletions(-)

--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -77,7 +77,7 @@ int __ext4_check_dir_entry(const char *f
else if (unlikely(rlen < EXT4_DIR_REC_LEN(de->name_len)))
error_msg = "rec_len is too small for name_len";
else if (unlikely(((char *) de - buf) + rlen > size))
- error_msg = "directory entry across range";
+ error_msg = "directory entry overrun";
else if (unlikely(le32_to_cpu(de->inode) >
le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count)))
error_msg = "inode out of bounds";
@@ -86,18 +86,16 @@ int __ext4_check_dir_entry(const char *f

if (filp)
ext4_error_file(filp, function, line, bh->b_blocknr,
- "bad entry in directory: %s - offset=%u(%u), "
- "inode=%u, rec_len=%d, name_len=%d",
- error_msg, (unsigned) (offset % size),
- offset, le32_to_cpu(de->inode),
- rlen, de->name_len);
+ "bad entry in directory: %s - offset=%u, "
+ "inode=%u, rec_len=%d, name_len=%d, size=%d",
+ error_msg, offset, le32_to_cpu(de->inode),
+ rlen, de->name_len, size);
else
ext4_error_inode(dir, function, line, bh->b_blocknr,
- "bad entry in directory: %s - offset=%u(%u), "
- "inode=%u, rec_len=%d, name_len=%d",
- error_msg, (unsigned) (offset % size),
- offset, le32_to_cpu(de->inode),
- rlen, de->name_len);
+ "bad entry in directory: %s - offset=%u, "
+ "inode=%u, rec_len=%d, name_len=%d, size=%d",
+ error_msg, offset, le32_to_cpu(de->inode),
+ rlen, de->name_len, size);

return 1;
}
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1741,6 +1741,7 @@ int empty_inline_dir(struct inode *dir,
{
int err, inline_size;
struct ext4_iloc iloc;
+ size_t inline_len;
void *inline_pos;
unsigned int offset;
struct ext4_dir_entry_2 *de;
@@ -1768,8 +1769,9 @@ int empty_inline_dir(struct inode *dir,
goto out;
}

+ inline_len = ext4_get_inline_size(dir);
offset = EXT4_INLINE_DOTDOT_SIZE;
- while (offset < dir->i_size) {
+ while (offset < inline_len) {
de = ext4_get_inline_entry(dir, &iloc, offset,
&inline_pos, &inline_size);
if (ext4_check_dir_entry(dir, NULL, de,