In the Linux kernel, the following vulnerability has been resolved:btrfs: fix race in read_extent_buffer_pages()There are reports from tree-checker that detects corrupted nodes,
without any obvious pattern so possibly an overwrite in memory.
After some debugging it turns out there's a race when reading an extent
buffer the uptodate status can be missed.To prevent concurrent reads for the same extent buffer,
read_extent_buffer_pages() performs these checks:At this point, it seems safe to start the actual read operation. Once
that completes, end_bbio_meta_read() doesNormally, this is enough to ensure only one read happens, and all other
callers wait for it to finish before returning.  Unfortunately, there is
a racey interleaving:When this happens, thread B kicks of an unnecessary read. Worse, thread
C will see UPTODATE set and return immediately, while the read from
thread B is still in progress.  This race could result in tree-checker
errors like this as the extent buffer is concurrently modified:Fix it by testing UPTODATE again after setting the READING bit, and if
it's been set, skip the unnecessary read.[ minor update of changelog ]