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Subject[PATCH 4.19 205/219] ext4: fix ext4_empty_dir() for directories with holes
Date
From: Jan Kara <jack@suse.cz>

commit 64d4ce892383b2ad6d782e080d25502f91bf2a38 upstream.

Function ext4_empty_dir() doesn't correctly handle directories with
holes and crashes on bh->b_data dereference when bh is NULL. Reorganize
the loop to use 'offset' variable all the times instead of comparing
pointers to current direntry with bh->b_data pointer. Also add more
strict checking of '.' and '..' directory entries to avoid entering loop
in possibly invalid state on corrupted filesystems.

CC: stable@vger.kernel.org
Fixes: 4e19d6b65fb4 ("ext4: allow directory holes")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191202170213.4761-2-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext4/namei.c | 32 ++++++++++++++++++--------------
1 file changed, 18 insertions(+), 14 deletions(-)

--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2693,7 +2693,7 @@ bool ext4_empty_dir(struct inode *inode)
{
unsigned int offset;
struct buffer_head *bh;
- struct ext4_dir_entry_2 *de, *de1;
+ struct ext4_dir_entry_2 *de;
struct super_block *sb;

if (ext4_has_inline_data(inode)) {
@@ -2718,19 +2718,25 @@ bool ext4_empty_dir(struct inode *inode)
return true;

de = (struct ext4_dir_entry_2 *) bh->b_data;
- de1 = ext4_next_entry(de, sb->s_blocksize);
- if (le32_to_cpu(de->inode) != inode->i_ino ||
- le32_to_cpu(de1->inode) == 0 ||
- strcmp(".", de->name) || strcmp("..", de1->name)) {
- ext4_warning_inode(inode, "directory missing '.' and/or '..'");
+ if (ext4_check_dir_entry(inode, NULL, de, bh, bh->b_data, bh->b_size,
+ 0) ||
+ le32_to_cpu(de->inode) != inode->i_ino || strcmp(".", de->name)) {
+ ext4_warning_inode(inode, "directory missing '.'");
brelse(bh);
return true;
}
- offset = ext4_rec_len_from_disk(de->rec_len, sb->s_blocksize) +
- ext4_rec_len_from_disk(de1->rec_len, sb->s_blocksize);
- de = ext4_next_entry(de1, sb->s_blocksize);
+ offset = ext4_rec_len_from_disk(de->rec_len, sb->s_blocksize);
+ de = ext4_next_entry(de, sb->s_blocksize);
+ if (ext4_check_dir_entry(inode, NULL, de, bh, bh->b_data, bh->b_size,
+ offset) ||
+ le32_to_cpu(de->inode) == 0 || strcmp("..", de->name)) {
+ ext4_warning_inode(inode, "directory missing '..'");
+ brelse(bh);
+ return true;
+ }
+ offset += ext4_rec_len_from_disk(de->rec_len, sb->s_blocksize);
while (offset < inode->i_size) {
- if ((void *) de >= (void *) (bh->b_data+sb->s_blocksize)) {
+ if (!(offset & (sb->s_blocksize - 1))) {
unsigned int lblock;
brelse(bh);
lblock = offset >> EXT4_BLOCK_SIZE_BITS(sb);
@@ -2741,12 +2747,11 @@ bool ext4_empty_dir(struct inode *inode)
}
if (IS_ERR(bh))
return true;
- de = (struct ext4_dir_entry_2 *) bh->b_data;
}
+ de = (struct ext4_dir_entry_2 *) (bh->b_data +
+ (offset & (sb->s_blocksize - 1)));
if (ext4_check_dir_entry(inode, NULL, de, bh,
bh->b_data, bh->b_size, offset)) {
- de = (struct ext4_dir_entry_2 *)(bh->b_data +
- sb->s_blocksize);
offset = (offset | (sb->s_blocksize - 1)) + 1;
continue;
}
@@ -2755,7 +2760,6 @@ bool ext4_empty_dir(struct inode *inode)
return false;
}
offset += ext4_rec_len_from_disk(de->rec_len, sb->s_blocksize);
- de = ext4_next_entry(de, sb->s_blocksize);
}
brelse(bh);
return true;

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