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isofs: validate directory records in isofs_read_level3_size()

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isofs_read_level3_size() walks the multi-extent directory records of a
file and dereferences de->size and de->flags for each one without ever
checking the record's length byte.  A record with a short length placed
near the end of a block makes those fixed-field reads run past the
record, and for a record at the end of the last block of a page, past
the buffer.

readdir, lookup and the NFS get_parent path have validated every record
with isofs_dir_record_valid() since commit e2ee4078ec ("isofs:
validate directory records consistently").  Do the same here, after
moving on to the next block when the previous record ended exactly at
the end of the block or the rest of the block is zero padding, as
commit 3c01d9263683 ("isofs: Fix handling of directories with tight
blocks") does for the other two walkers.

The check rejects a record that would run past its block, so the code
that reassembled such a record from two blocks can no longer run.
ECMA-119 does not allow directory records to straddle sector
boundaries, which is what commit b2eb2e2886 ("isofs: Drop support of
directory entries straddling blocks") relied on when it removed the
same code from readdir and lookup.  Remove it here too, along with its
temporary record buffer.

Found by fuzzing fs/isofs in a userspace harness with ASan
(heap-buffer-overflow reads in de->flags).

Signed-off-by: Matthias Goergens <matthias.goergens@gmail.com>
Link: https://patch.msgid.link/20260923153220.777907-1-matthias.goergens@gmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Matthias Goergens 2026-09-23 23:32:20 +08:00 committed by Jan Kara
parent a4ed759939
commit 6e69419ca6
1 changed files with 13 additions and 31 deletions
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44
fs/isofs/inode.c
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@ -1176,7 +1176,6 @@ static int isofs_read_level3_size(struct inode *inode)
unsigned long block, offset, block_saved, offset_saved;
int i = 0;
int more_entries = 0;
struct iso_directory_record *tmpde = NULL;
struct iso_inode_info *ei = ISOFS_I(inode);
inode->i_size = 0;
@ -1200,9 +1199,12 @@ static int isofs_read_level3_size(struct inode *inode)
goto out_noread;
}
de = (struct iso_directory_record *) (bh->b_data + offset);
de_len = *(unsigned char *) de;
if (de_len == 0) {
/*
* If we are at the end of a block (or at its zero-padded
* tail), move on to the next block.
*/
if (offset >= bufsize || de->length[0] == 0) {
brelse(bh);
bh = NULL;
++block;
@ -1210,32 +1212,18 @@ static int isofs_read_level3_size(struct inode *inode)
continue;
}
if (!isofs_dir_record_valid(de, offset, bufsize)) {
printk(KERN_NOTICE "iso9660: Corrupted directory entry in block %lu of inode %llu\n",
block, inode->i_ino);
brelse(bh);
return -EIO;
}
de_len = de->length[0];
block_saved = block;
offset_saved = offset;
offset += de_len;
/* Make sure we have a full directory entry */
if (offset >= bufsize) {
int slop = bufsize - offset + de_len;
if (!tmpde) {
tmpde = kmalloc(256, GFP_KERNEL);
if (!tmpde)
goto out_nomem;
}
memcpy(tmpde, de, slop);
offset &= bufsize - 1;
block++;
brelse(bh);
bh = NULL;
if (offset) {
bh = sb_bread(inode->i_sb, block);
if (!bh)
goto out_noread;
memcpy((void *)tmpde+slop, bh->b_data, offset);
}
de = tmpde;
}
inode->i_size += isonum_733(de->size);
if (i == 1) {
ei->i_next_section_block = block_saved;
@ -1249,17 +1237,11 @@ static int isofs_read_level3_size(struct inode *inode)
goto out_toomany;
} while (more_entries);
out:
kfree(tmpde);
brelse(bh);
return 0;
out_nomem:
brelse(bh);
return -ENOMEM;
out_noread:
printk(KERN_INFO "ISOFS: unable to read i-node block %lu\n", block);
kfree(tmpde);
return -EIO;
out_toomany: