tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
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hfs: Sanity check the root record

In the syzbot reproducer, the hfs_cat_rec for the root dir has type
HFS_CDR_FIL after being read with hfs_bnode_read() in hfs_super_fill().
This indicates it should be used as an hfs_cat_file, which is 102 bytes.
Only the first 70 bytes of that struct are initialized, however,
because the entrylength passed into hfs_bnode_read() is still the length of
a directory record. This causes uninitialized values to be used later on,
when the hfs_cat_rec union is treated as the larger hfs_cat_file struct.

Add a check to make sure the retrieved record has the correct type
for the root directory (HFS_CDR_DIR), and make sure we load the correct
number of bytes for a directory record.

Reported-by: syzbot+2db3c7526ba68f4ea776@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2db3c7526ba68f4ea776
Tested-by: syzbot+2db3c7526ba68f4ea776@syzkaller.appspotmail.com
Tested-by: Leo Stone <leocstone@gmail.com>
Signed-off-by: Leo Stone <leocstone@gmail.com>
Link: https://lore.kernel.org/r/20241201051420.77858-1-leocstone@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

authored by

Leo Stone and committed by
Christian Brauner b905bafd 40384c84

+3 -1
+3 -1
fs/hfs/super.c
··· 349 349 goto bail_no_root; 350 350 res = hfs_cat_find_brec(sb, HFS_ROOT_CNID, &fd); 351 351 if (!res) { 352 - if (fd.entrylength > sizeof(rec) || fd.entrylength < 0) { 352 + if (fd.entrylength != sizeof(rec.dir)) { 353 353 res = -EIO; 354 354 goto bail_hfs_find; 355 355 } 356 356 hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength); 357 + if (rec.type != HFS_CDR_DIR) 358 + res = -EIO; 357 359 } 358 360 if (res) 359 361 goto bail_hfs_find;