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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <67e57c41.050a0220.2f068f.0034.GAE@google.com> References: <67e57c41.050a0220.2f068f.0034.GAE@google.com> To: syzbot Cc: dhowells@redhat.com, linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org, marc.dionne@auristor.com, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [afs?] BUG: sleeping function called from invalid context in __alloc_frozen_pages_noprof Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <103745.1743241743.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Sat, 29 Mar 2025 09:49:03 +0000 Message-ID: <103746.1743241743@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.gi= t master commit db7a516159869b19f237c73bd75599bbe0bfcc4d Author: David Howells Date: Fri Mar 28 16:46:58 2025 +0000 afs: Fix afs_dynroot_readdir() to not use the RCU read lock = afs_dynroot_readdir() uses the RCU read lock to walk the cell list whi= lst emitting cell automount entries - but dir_emit() may write to a usersp= ace buffer, thereby causing a fault to occur and waits to happen. = Fix afs_dynroot_readdir() to get a shared lock on net->cells_lock inst= ead. = Fixes: 1d0b929fc070 ("afs: Change dynroot to create contents on demand= ") Reported-by: syzbot+3b6c5c6a1d0119b687a1@syzkaller.appspotmail.com Signed-off-by: David Howells cc: Marc Dionne cc: linux-afs@lists.infradead.org cc: linux-fsdevel@vger.kernel.org diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c index 691e0ae607a1..8c6130789fde 100644 --- a/fs/afs/dynroot.c +++ b/fs/afs/dynroot.c @@ -348,9 +348,9 @@ static int afs_dynroot_readdir(struct file *file, stru= ct dir_context *ctx) } = if ((unsigned long long)ctx->pos <=3D AFS_MAX_DYNROOT_CELL_INO) { - rcu_read_lock(); + down_read(&net->cells_lock); ret =3D afs_dynroot_readdir_cells(net, ctx); - rcu_read_unlock(); + up_read(&net->cells_lock); } return ret; }