CVE-2024-26982

In the Linux kernel, the following vulnerability has been resolved:

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

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

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. Fillmetaindex() is called to allocate (via emptymetaindex()) 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 fillmetaindex() is subsequently called again on another read operation, locatemetaindex() 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]