AZL-99510

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

nilfs2: reject invalid block index in GC ioctl

Syzbot reported list corruption caused by a double listaddtail() call on bh->bassocbuffers within nilfslookupdirtydatabuffers().

Analysis revealed that the root cause was the insertion of a page/folio with a page index of ULONGMAX into the page cache via the GC ioctl. filemapgetfoliostag(), called by nilfslookupdirtydatabuffers(), repeatedly detects a dirty folio with a page index of ULONG_MAX due to index wrap-around, leading to duplicate processing of dirty buffers.

As a preparatory step, the GC ioctl loads the page/folio of the block to be moved during GC and inserts it into the page cache based on information in the nilfsvdesc structure passed as an argument. Normally, this does not cause issues because the user-space GC library configures the nilfsvdesc structure properly. However, since there is no range check on the parameters determining the page index, a request with artificially crafted parameters -- such as those generated by Syzbot -- can result in a page/folio being inserted with a page index of ULONG_MAX, triggering the above problem.

This resolves the issue by checking the ranges of 'vdoffset' and 'vdvblocknr' in the nilfs_vdesc structure that determine the page index, thereby preventing the invalid page/folio insertions.