From: "Jason A. Donenfeld" <ja...@zx2c4.com> Date: Wed, 9 Sep 2020 13:58:13 +0200
> Yesterday, Eric reported a race condition found by syzbot. This series > contains two commits, one that fixes the direct issue, and another that > addresses the more general issue, as a defense in depth. > > 1) The basic problem syzbot unearthed was that one particular mutation > of handshake->entry was not protected by the handshake mutex like the > other cases, so this patch basically just reorders a line to make > sure the mutex is actually taken at the right point. Most of the work > here went into making sure the race was fully understood and making a > reproducer (which syzbot was unable to do itself, due to the rarity > of the race). > > 2) Eric's initial suggestion for fixing this was taking a spinlock > around the hash table replace function where the null ptr deref was > happening. This doesn't address the main problem in the most precise > possible way like (1) does, but it is a good suggestion for > defense-in-depth, in case related issues come up in the future, and > basically costs nothing from a performance perspective. I thought it > aided in implementing a good general rule: all mutators of that hash > table take the table lock. So that's part of this series as a > companion. > > Both of these contain Fixes: tags and are good candidates for stable. Series applied and queued up for -stable, thanks.
