linux-kernel - [PATCH] overlayfs: retry when getting the dentry fid fails due to lack of memory

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Message-ID: <tencent_451BB425FBBAC7BB5833E59EA31B4D4B0708@qq.com>
Date: Wed, 30 Oct 2024 21:30:29 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+ec07f6f5ce62b858579f@...kaller.appspotmail.com
Cc: amir73il@...il.com,
	linux-kernel@...r.kernel.org,
	linux-unionfs@...r.kernel.org,
	miklos@...redi.hu,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH] overlayfs: retry when getting the dentry fid fails due to lack of memory

Syzbot report a WARNING in ovl_encode_real_fh.
When the memory is insufficient, the allocation of fh fails, which causes
the failure to obtain the dentry fid, and finally causes the dentry encoding
to fail.
Retry is used to avoid the failure of fh allocation caused by temporary
insufficient memory.

Reported-and-tested-by: syzbot+ec07f6f5ce62b858579f@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ec07f6f5ce62b858579f
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
 fs/overlayfs/copy_up.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 2ed6ad641a20..1e027a3cf084 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -423,15 +423,22 @@ struct ovl_fh *ovl_encode_real_fh(struct ovl_fs *ofs, struct dentry *real,
 	int fh_type, dwords;
 	int buflen = MAX_HANDLE_SZ;
 	uuid_t *uuid = &real->d_sb->s_uuid;
-	int err;
+	int err, rtt = 0;
 
 	/* Make sure the real fid stays 32bit aligned */
 	BUILD_BUG_ON(OVL_FH_FID_OFFSET % 4);
 	BUILD_BUG_ON(MAX_HANDLE_SZ + OVL_FH_FID_OFFSET > 255);
 
+retry:
 	fh = kzalloc(buflen + OVL_FH_FID_OFFSET, GFP_KERNEL);
-	if (!fh)
+	if (!fh) {
+		if (!rtt) {
+			cond_resched();
+			rtt++;
+			goto retry;
+		}
 		return ERR_PTR(-ENOMEM);
+	}
 
 	/*
 	 * We encode a non-connectable file handle for non-dir, because we
-- 
2.43.0