[PATCH 6.8 150/158] Squashfs: check the inode number is not the invalid value of zero

Greg Kroah-Hartman
2024-04-23T21:42:30Z

From: Phillip Lougher <phillip@squashfs.org.uk>

commit 9253c54e01b6505d348afbc02abaa4d9f8a01395 upstream.

Syskiller has produced an out of bounds access in fill_meta_index().

That out of bounds access is ultimately caused because the inode
has an inode number with the invalid value of zero, which was not checked.

The reason this causes the out of bounds access is due to following
sequence of events:

1. Fill_meta_index() is called to allocate (via empty_meta_index())
and fill a metadata index. It however suffers a data read error
and aborts, invalidating the newly returned empty metadata index.
It does this by setting the inode number of the index to zero,
which means unused (zero is not a valid inode number).

2. When fill_meta_index() is subsequently called again on another
read operation, locate_meta_index() returns the previous index
because it matches the inode number of 0. Because this index
has been returned it is expected to have been filled, and because
it hasn't been, an out of bounds access is performed.

This patch adds a sanity check which checks that the inode number
is not zero when the inode is created and returns -EINVAL if it is.

[phillip@squashfs.org.uk: whitespace fix]
Link: https://lkml.kernel.org/r/20240409204723.446925-1-phillip@squashfs.org.uk
Link: https://lkml.kernel.org/r/20240408220206.435788-1-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: "Ubisectech Sirius" <bugreport@ubisectech.com>
Closes: https://lore.kernel.org/lkml/87f5c007-b8a5-41ae-8b57-431e924c5915.bugreport@ubisectech.com/
Cc: Christian Brauner <brauner@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/squashfs/inode.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/fs/squashfs/inode.c
+++ b/fs/squashfs/inode.c
@@ -48,6 +48,10 @@ static int squashfs_new_inode(struct sup
gid_t i_gid;
int err;

+ inode->i_ino = le32_to_cpu(sqsh_ino->inode_number);
+ if (inode->i_ino == 0)
+ return -EINVAL;
+
err = squashfs_get_id(sb, le16_to_cpu(sqsh_ino->uid), &i_uid);
if (err)
return err;
@@ -58,7 +62,6 @@ static int squashfs_new_inode(struct sup

i_uid_write(inode, i_uid);
i_gid_write(inode, i_gid);
- inode->i_ino = le32_to_cpu(sqsh_ino->inode_number);
inode_set_mtime(inode, le32_to_cpu(sqsh_ino->mtime), 0);
inode_set_atime(inode, inode_get_mtime_sec(inode), 0);
inode_set_ctime(inode, inode_get_mtime_sec(inode), 0);