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authorMiklos Szeredi <mszeredi@redhat.com>2021-07-28 11:38:43 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2021-08-10 11:21:30 +0300
commit9b91b6b019fda817eb52f728eb9c79b3579760bc (patch)
treeff9d912e8f6943cc084d9a8160def07e50225378 /fs/overlayfs
parent9011c2791e63fc05721b545c41ad025d8073566e (diff)
downloadlinux-9b91b6b019fda817eb52f728eb9c79b3579760bc.tar.xz
ovl: fix deadlock in splice write
There's possibility of an ABBA deadlock in case of a splice write to an overlayfs file and a concurrent splice write to a corresponding real file. The call chain for splice to an overlay file: -> do_splice [takes sb_writers on overlay file] -> do_splice_from -> iter_file_splice_write [takes pipe->mutex] -> vfs_iter_write ... -> ovl_write_iter [takes sb_writers on real file] And the call chain for splice to a real file: -> do_splice [takes sb_writers on real file] -> do_splice_from -> iter_file_splice_write [takes pipe->mutex] Syzbot successfully bisected this to commit 82a763e61e2b ("ovl: simplify file splice"). Fix by reverting the write part of the above commit and by adding missing bits from ovl_write_iter() into ovl_splice_write(). Fixes: 82a763e61e2b ("ovl: simplify file splice") Reported-and-tested-by: syzbot+579885d1a9a833336209@syzkaller.appspotmail.com Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs')
-rw-r--r--fs/overlayfs/file.c47
1 files changed, 46 insertions, 1 deletions
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 4d53d3b7e5fe..d081faa55e83 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -392,6 +392,51 @@ out_unlock:
return ret;
}
+/*
+ * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
+ * due to lock order inversion between pipe->mutex in iter_file_splice_write()
+ * and file_start_write(real.file) in ovl_write_iter().
+ *
+ * So do everything ovl_write_iter() does and call iter_file_splice_write() on
+ * the real file.
+ */
+static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
+ loff_t *ppos, size_t len, unsigned int flags)
+{
+ struct fd real;
+ const struct cred *old_cred;
+ struct inode *inode = file_inode(out);
+ struct inode *realinode = ovl_inode_real(inode);
+ ssize_t ret;
+
+ inode_lock(inode);
+ /* Update mode */
+ ovl_copyattr(realinode, inode);
+ ret = file_remove_privs(out);
+ if (ret)
+ goto out_unlock;
+
+ ret = ovl_real_fdget(out, &real);
+ if (ret)
+ goto out_unlock;
+
+ old_cred = ovl_override_creds(inode->i_sb);
+ file_start_write(real.file);
+
+ ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
+
+ file_end_write(real.file);
+ /* Update size */
+ ovl_copyattr(realinode, inode);
+ revert_creds(old_cred);
+ fdput(real);
+
+out_unlock:
+ inode_unlock(inode);
+
+ return ret;
+}
+
static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
struct fd real;
@@ -603,7 +648,7 @@ const struct file_operations ovl_file_operations = {
.fadvise = ovl_fadvise,
.flush = ovl_flush,
.splice_read = generic_file_splice_read,
- .splice_write = iter_file_splice_write,
+ .splice_write = ovl_splice_write,
.copy_file_range = ovl_copy_file_range,
.remap_file_range = ovl_remap_file_range,