Messages in this thread | | | Date | Wed, 21 Apr 2021 17:03:24 +0000 | From | Al Viro <> | Subject | Re: [PATCH 053/190] Revert "ecryptfs: replace BUG_ON with error handling code" |
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On Wed, Apr 21, 2021 at 11:13:29AM -0500, Tyler Hicks wrote:
> > It *is* functionally harmless, AFAICS, but only because the condition > > is really impossible. However, > > * it refers to vague (s)tool they'd produced, nevermind that > > all they really do is "find BUG_ON(), replace with returning an error". > > * unlike BUG_ON(), the replacement does *NOT* document the > > fact that condition should be impossible. > > IMO either should be sufficient for rejecting the patch. > > I agree that it was not a malicious change. There are other places > within the same function that return -EINVAL and the expectation is that > errors from this function should be handled safely.
Umm... Assuming that failure exits in the callers will function properly if those conditions are true. Which is not obvious at all.
> That said, I can find no real-world reports of this BUG_ON() ever being > a problem and I don't think that there's any actual need for this > change. So, I'm alright with it being reverted considering the > circumstances.
AFAICS, at least some parts of that BUG_ON() are provably impossible (e.g. NULL crypt_stat would've oopsed well upstream of the only call of that function). ECRYPTFS_STRUCT_INITIALIZED is set after ecryptfs_alloc_inode() and never cleared, i.e. it should be present in ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat.flags for all inodes. And crypt_stat we are passing to that thing is calculated as &(ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat), which is another reason why it can't be NULL.
Incidentally, what's ecryptfs_setattr() doing with similar check? It had been introduced in e10f281bca03 "eCryptfs: initialize crypt_stat in setattr", which claims Recent changes in eCryptfs have made it possible to get to ecryptfs_setattr() with an uninitialized crypt_stat struct. This results in a wide and colorful variety of unpleasantries. This patch properly initializes the crypt_stat structure in ecryptfs_setattr() when it is necessary to do so. and AFAICS at that point the call of ecryptfs_init_crypt_stat() in ecryptfs_alloc_inode() had already been there and EXCRYPTFS_STRUCT_INITIALIZED had been (unconditionally) set by it. So how could that check trigger in ecryptfs_setattr()? No direct calls of that function (then as well as now), it's only reachable as ecryptfs_{symlink,dir,main}_iops.setattr. The first two could only end up set by ecryptfs_interpose(), for inode returned by iget5_locked() (i.e. one that had been returned by ->alloc_inode()), the last is set by ecryptfs_init_inode(), called by ecryptfs_inode_set(), passed as callback to iget5_locked() by the same ecryptfs_interpose(). IOW, again, the inode must have been returned by ->alloc_inode().
I realize that it had been a long time ago, but... could somebody recall what that patch had been about? Michael?
Commit in question contains another (and much bigger) chunk; do the comments in commit message refer to it? Because it really looks like if (!(crypt_stat->flags & ECRYPTFS_STRUCT_INITIALIZED)) ecryptfs_init_crypt_stat(crypt_stat); part in ecryptfs_setattr() is a confusing no-op...
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