Squashfs: check the inode number is not the invalid value of zero

JIRA: https://issues.redhat.com/browse/RHEL-35098
CVE: CVE-2024-26982
Upstream Status: From upstream linux mainline

commit 9253c54
Author: Phillip Lougher <phillip@squashfs.org.uk>
Date:   Mon Apr 8 23:02:06 2024 +0100

    Squashfs: check the inode number is not the invalid value of zero

    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: Abhi Das <adas@redhat.com>

Author: Abhi Das

fs/squashfs/inode.c

@@ -48,6 +48,10 @@ static int squashfs_new_inode(struct super_block *sb, struct inode *inode,
 	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 super_block *sb, struct inode *inode,
 
 	i_uid_write(inode, i_uid);
 	i_gid_write(inode, i_gid);
-	inode->i_ino = le32_to_cpu(sqsh_ino->inode_number);
 	inode->i_mtime.tv_sec = le32_to_cpu(sqsh_ino->mtime);
 	inode->i_atime.tv_sec = inode->i_mtime.tv_sec;
 	inode->i_ctime.tv_sec = inode->i_mtime.tv_sec;