From: NeilBrown <neilb@suse.com>
To: "J. Bruce Fields" <bfields@fieldses.org>,
Jeff Layton <jlayton@kernel.org>
Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] nfsd: fix memory corruption caused by readdir
Date: Mon, 04 Mar 2019 14:08:22 +1100 [thread overview]
Message-ID: <87lg1vs5eh.fsf@notabene.neil.brown.name> (raw)
[-- Attachment #1: Type: text/plain, Size: 3242 bytes --]
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 fix 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
boundary).
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
corrupted.
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
nfsd3_proc_readdir.
(Note that the commit hash in the Fixes tag is from the 'history'
tree - this bug predates git).
Fixes: eb229d253e6c ("[PATCH] kNFSd: fix two xdr-encode bugs for readdirplus reply")
Cc: stable@vger.kernel.org (v2.6.12+)
Signed-off-by: NeilBrown <neilb@suse.com>
---
Can I still get extra credit for fixing a bug that is 14.5 years old, if
I'm the one who introduced it?
fs/nfsd/nfs3proc.c | 16 ++++++++++++++--
fs/nfsd/nfs3xdr.c | 1 +
2 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 9eb8086ea841..c9cf46e0c040 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -463,8 +463,19 @@ nfsd3_proc_readdir(struct svc_rqst *rqstp)
&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;
+ }
RETURN_STATUS(nfserr);
}
@@ -533,6 +544,7 @@ nfsd3_proc_readdirplus(struct svc_rqst *rqstp)
} else {
xdr_encode_hyper(resp->offset, offset);
}
+ resp->offset = NULL;
}
RETURN_STATUS(nfserr);
diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index 9b973f4f7d01..83919116d5cb 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -921,6 +921,7 @@ encode_entry(struct readdir_cd *ccd, const char *name, int namlen,
} else {
xdr_encode_hyper(cd->offset, offset64);
}
+ cd->offset = NULL;
}
/*
--
2.14.0.rc0.dirty
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]
next reply other threads:[~2019-03-04 3:08 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-04 3:08 NeilBrown [this message]
2019-03-04 16:47 ` [PATCH] nfsd: fix memory corruption caused by readdir J. Bruce Fields
2019-03-04 23:48 ` NeilBrown
2019-03-05 21:42 ` J. Bruce Fields
2019-03-06 22:49 ` [PATCH] nfsd: allow nfsv3 readdir request to be larger NeilBrown
2019-03-08 19:29 ` J. Bruce Fields
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87lg1vs5eh.fsf@notabene.neil.brown.name \
--to=neilb@suse.com \
--cc=bfields@fieldses.org \
--cc=jlayton@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nfs@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).