From 6e69419ca6a4bfc3f3445ab139fd07a0e9cf74be Mon Sep 17 00:00:00 2001 From: Matthias Goergens Date: Wed, 23 Sep 2026 23:32:20 +0800 Subject: [PATCH] isofs: validate directory records in isofs_read_level3_size() 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 e2ee4078ec58 ("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 b2eb2e288604 ("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 Link: https://patch.msgid.link/20260923153220.777907-1-matthias.goergens@gmail.com Signed-off-by: Jan Kara --- fs/isofs/inode.c | 44 +++++++++++++------------------------------- 1 file changed, 13 insertions(+), 31 deletions(-) diff --git a/fs/isofs/inode.c b/fs/isofs/inode.c index b766b5c9c593..184350d2e6ad 100644 --- a/fs/isofs/inode.c +++ b/fs/isofs/inode.c @@ -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: