1.8 KiB
CVE-2025-38691
Description
In the Linux kernel, the following vulnerability has been resolved:pNFS: Fix uninited ptr deref in block/scsi layoutThe error occurs on the third attempt to encode extents. When functionext_tree_prepare_commit() reallocates a larger buffer to retry encodingextents, the "layoutupdate_pages" page array is initialized only after theretry loop. But ext_tree_free_commitdata() is called on every iterationand tries to put pages in the array, thus dereferencing uninitializedpointers.An additional problem is that there is no limit on the maximum possiblebuffer_size. When there are too many extents, the client may create alayoutcommit that is larger than the maximum possible RPC size acceptedby the server.During testing, we observed two typical scenarios. First, one memory pagefor extents is enough when we work with small files, append data to theend of the file, or preallocate extents before writing. But when we filla new large file without preallocating, the number of extents can be huge,and counting the number of written extents in ext_tree_encode_commit()does not help much. Since this number increases even more betweenunlocking and locking of ext_tree, the reallocated buffer may not belarge enough again and again.
POC
Reference
No PoCs from references.