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authorDavid Howells <dhowells@redhat.com>2023-07-04 20:22:15 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2023-07-04 12:24:32 -0700
commit03275585cabd0240944f19f33d7584a1b099a3a8 (patch)
tree21627f14ab70a66fef1aafac26862e85e2e97bb2 /fs
parent538140ca602b1c5f3870bef051c93b491045f70a (diff)
afs: Fix accidental truncation when storing data
When an AFS FS.StoreData RPC call is made, amongst other things it is given the resultant file size to be. On the server, this is processed by truncating the file to new size and then writing the data. Now, kafs has a lock (vnode->io_lock) that serves to serialise operations against a specific vnode (ie. inode), but the parameters for the op are set before the lock is taken. This allows two writebacks (say sync and kswapd) to race - and if writes are ongoing the writeback for a later write could occur before the writeback for an earlier one if the latter gets interrupted. Note that afs_writepages() cannot take i_mutex and only takes a shared lock on vnode->validate_lock. Also note that the server does the truncation and the write inside a lock, so there's no problem at that end. Fix this by moving the calculation for the proposed new i_size inside the vnode->io_lock. Also reset the iterator (which we might have read from) and update the mtime setting there. Fixes: bd80d8a80e12 ("afs: Use ITER_XARRAY for writing") Reported-by: Marc Dionne <marc.dionne@auristor.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeffrey Altman <jaltman@auristor.com> Reviewed-by: Marc Dionne <marc.dionne@auristor.com> cc: linux-afs@lists.infradead.org cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/r/3526895.1687960024@warthog.procyon.org.uk/ Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/afs/write.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 9c7fd6fd8095..e1c45341719b 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -413,17 +413,19 @@ static int afs_store_data(struct afs_vnode *vnode, struct iov_iter *iter, loff_t
afs_op_set_vnode(op, 0, vnode);
op->file[0].dv_delta = 1;
op->file[0].modification = true;
- op->store.write_iter = iter;
op->store.pos = pos;
op->store.size = size;
- op->store.i_size = max(pos + size, vnode->netfs.remote_i_size);
op->store.laundering = laundering;
- op->mtime = vnode->netfs.inode.i_mtime;
op->flags |= AFS_OPERATION_UNINTR;
op->ops = &afs_store_data_operation;
try_next_key:
afs_begin_vnode_operation(op);
+
+ op->store.write_iter = iter;
+ op->store.i_size = max(pos + size, vnode->netfs.remote_i_size);
+ op->mtime = vnode->netfs.inode.i_mtime;
+
afs_wait_for_operation(op);
switch (op->error) {