nfs/localio: fix regression due to out-of-order __put_cred

commit 3af870aedbff10bfed220e280b57a405e972229f upstream.

Commit f2060bdc21d7 ("nfs/localio: add refcounting for each iocb IO
associated with NFS pgio header") inadvertantly reintroduced the same
potential for __put_cred() triggering BUG_ON(cred == current->cred) that
commit 992203a1fba5 ("nfs/localio: restore creds before releasing pageio
data") fixed.

Fix this by saving and restoring the cred around each {read,write}_iter
call within the respective for loop of nfs_local_call_{read,write} using
scoped_with_creds().

NOTE: this fix started by first reverting the following commits:

 94afb627dfc2 ("nfs: use credential guards in nfs_local_call_read()")
 bff3c841f7bd ("nfs: use credential guards in nfs_local_call_write()")
 1d18101a644e ("Merge tag 'kernel-6.19-rc1.cred' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs")

followed by narrowly fixing the cred lifetime issue by using
scoped_with_creds().  In doing so, this commit's changes appear more
extensive than they really are (as evidenced by comparing to v6.18's
fs/nfs/localio.c).

Reported-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Acked-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/linux-next/20251205111942.4150b06f@canb.auug.org.au/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
index b98bb292fef0cc364eadc34b747991d1b7fae680..ed2a7efaf8f20cf4064a6dbec0b434a7f3727749 100644 (file)
--- a/fs/nfs/localio.c
+++ b/fs/nfs/localio.c
@@ -623,8 +623,6 @@ static void nfs_local_call_read(struct work_struct *work)
        ssize_t status;
        int n_iters;
 
-       save_cred = override_creds(filp->f_cred);
-
        n_iters = atomic_read(&iocb->n_iters);
        for (int i = 0; i < n_iters ; i++) {
                if (iocb->iter_is_dio_aligned[i]) {
@@ -637,7 +635,10 @@ static void nfs_local_call_read(struct work_struct *work)
                } else
                        iocb->kiocb.ki_flags &= ~IOCB_DIRECT;
 
+               save_cred = override_creds(filp->f_cred);
                status = filp->f_op->read_iter(&iocb->kiocb, &iocb->iters[i]);
+               revert_creds(save_cred);
+
                if (status != -EIOCBQUEUED) {
                        if (unlikely(status >= 0 && status < iocb->iters[i].count))
                                force_done = true; /* Partial read */
@@ -647,8 +648,6 @@ static void nfs_local_call_read(struct work_struct *work)
                        }
                }
        }
-
-       revert_creds(save_cred);
 }
 
 static int
@@ -830,7 +829,6 @@ static void nfs_local_call_write(struct work_struct *work)
        int n_iters;
 
        current->flags |= PF_LOCAL_THROTTLE | PF_MEMALLOC_NOIO;
-       save_cred = override_creds(filp->f_cred);
 
        file_start_write(filp);
        n_iters = atomic_read(&iocb->n_iters);
@@ -845,7 +843,10 @@ static void nfs_local_call_write(struct work_struct *work)
                } else
                        iocb->kiocb.ki_flags &= ~IOCB_DIRECT;
 
+               save_cred = override_creds(filp->f_cred);
                status = filp->f_op->write_iter(&iocb->kiocb, &iocb->iters[i]);
+               revert_creds(save_cred);
+
                if (status != -EIOCBQUEUED) {
                        if (unlikely(status >= 0 && status < iocb->iters[i].count))
                                force_done = true; /* Partial write */
@@ -857,7 +858,6 @@ static void nfs_local_call_write(struct work_struct *work)
        }
        file_end_write(filp);
 
-       revert_creds(save_cred);
        current->flags = old_flags;
 }