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Date:   Fri, 22 Mar 2019 12:16:00 +0100
From:   Greg Kroah-Hartman <>
Cc:     Greg Kroah-Hartman <>,, NeilBrown <>,
        "J. Bruce Fields" <>
Subject: [PATCH 4.4 222/230] nfsd: fix memory corruption caused by readdir

4.4-stable review patch.  If anyone has any objections, please let me know.


From: NeilBrown <>

commit b602345da6cbb135ba68cf042df8ec9a73da7981 upstream.

If the result of an NFSv3 readdir{,plus} request results in the
"offset" on one entry having to be split across 2 pages, and is sized
so that the next directory entry doesn't fit in the requested size,
then memory corruption can happen.

When encode_entry() is called after encoding the last entry that fits,
it notices that ->offset and ->offset1 are set, and so stores the
offset value in the two pages as required.  It clears ->offset1 but
*does not* clear ->offset.

Normally this omission doesn't matter as encode_entry_baggage() will
be called, and will set ->offset to a suitable value (not on a page
But in the case where cd->buflen < elen and nfserr_toosmall is
returned, ->offset is not reset.

This means that nfsd3proc_readdirplus will see ->offset with a value 4
bytes before the end of a page, and ->offset1 set to NULL.
It will try to write 8bytes to ->offset.
If we are lucky, the next page will be read-only, and the system will
  BUG: unable to handle kernel paging request at...

If we are unlucky, some innocent page will have the first 4 bytes

nfsd3proc_readdir() doesn't even check for ->offset1, it just blindly
writes 8 bytes to the offset wherever it is.

Fix this by clearing ->offset after it is used, and copying the
->offset handling code from nfsd3_proc_readdirplus into

(Note that the commit hash in the Fixes tag is from the 'history'
 tree - this bug predates git).

Fixes: 0b1d57cf7654 ("[PATCH] kNFSd: Fix nfs3 dentry encoding")
Cc: (v2.6.12+)
Signed-off-by: NeilBrown <>
Signed-off-by: J. Bruce Fields <>
Signed-off-by: Greg Kroah-Hartman <>

 fs/nfsd/nfs3proc.c |   16 ++++++++++++++--
 fs/nfsd/nfs3xdr.c  |    1 +
 2 files changed, 15 insertions(+), 2 deletions(-)

--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -430,8 +430,19 @@ nfsd3_proc_readdir(struct svc_rqst *rqst
 					&resp->common, nfs3svc_encode_entry);
 	memcpy(resp->verf, argp->verf, 8);
 	resp->count = resp->buffer - argp->buffer;
-	if (resp->offset)
-		xdr_encode_hyper(resp->offset, argp->cookie);
+	if (resp->offset) {
+		loff_t offset = argp->cookie;
+		if (unlikely(resp->offset1)) {
+			/* we ended up with offset on a page boundary */
+			*resp->offset = htonl(offset >> 32);
+			*resp->offset1 = htonl(offset & 0xffffffff);
+			resp->offset1 = NULL;
+		} else {
+			xdr_encode_hyper(resp->offset, offset);
+		}
+		resp->offset = NULL;
+	}
@@ -499,6 +510,7 @@ nfsd3_proc_readdirplus(struct svc_rqst *
 		} else {
 			xdr_encode_hyper(resp->offset, offset);
+		resp->offset = NULL;
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -898,6 +898,7 @@ encode_entry(struct readdir_cd *ccd, con
 		} else {
 			xdr_encode_hyper(cd->offset, offset64);
+		cd->offset = NULL;

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