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Subject: [PATCH v2 1/5] NFSD: Fix ia_size underflow
From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Date:   Mon, 31 Jan 2022 13:24:46 -0500
Message-ID: <164365348686.3304.5808030961715602906.stgit@bazille.1015granger.net>
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References: <164365324981.3304.4571955521912946906.stgit@bazille.1015granger.net>
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iattr::ia_size is a loff_t, which is a signed 64-bit type. NFSv3 and
NFSv4 both define file size as an unsigned 64-bit type. Thus there
is a range of valid file size values an NFS client can send that is
already larger than Linux can handle.

Currently decode_fattr4() dumps a full u64 value into ia_size. If
that value happens to be larger than S64_MAX, then ia_size
underflows. I'm about to fix up the NFSv3 behavior as well, so let's
catch the underflow in the common code path: nfsd_setattr().

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/vfs.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 99c2b9dfbb10..0cccceb105e7 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -435,6 +435,10 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
 			.ia_size	= iap->ia_size,
 		};
 
+		host_err = -EFBIG;
+		if (iap->ia_size < 0)
+			goto out_unlock;
+
 		host_err = notify_change(&init_user_ns, dentry, &size_attr, NULL);
 		if (host_err)
 			goto out_unlock;