From: Fedor Pchelkin <pchelkin@ispras.ru>
To: Christian Schoenebeck <linux_oss@crudebyte.com>
Cc: Dominique Martinet <asmadeus@codewreck.org>,
Latchesar Ionkov <lucho@ionkov.net>,
Eric Van Hensbergen <ericvh@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>,
v9fs@lists.linux.dev, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
Alexey Khoroshilov <khoroshilov@ispras.ru>,
lvc-project@linuxtesting.org
Subject: Re: [PATCH v2] net: 9p: avoid freeing uninit memory in p9pdu_vreadf
Date: Tue, 5 Dec 2023 16:09:49 +0300 [thread overview]
Message-ID: <9f21f00b-0806-4811-8d0a-9b6175eaedeb-pchelkin@ispras.ru> (raw)
In-Reply-To: <1741521.OAD31uVnNo@silver>
On 23/12/05 01:29PM, Christian Schoenebeck wrote:
> On Tuesday, December 5, 2023 10:19:50 AM CET Fedor Pchelkin wrote:
> > If an error occurs while processing an array of strings in p9pdu_vreadf
> > then uninitialized members of *wnames array are freed.
> >
> > Fix this by iterating over only lower indices of the array. Also handle
> > possible uninit *wnames usage if first p9pdu_readf() call inside 'T' case
> > fails.
> >
> > Found by Linux Verification Center (linuxtesting.org).
> >
> > Fixes: ace51c4dd2f9 ("9p: add new protocol support code")
> > Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
> > ---
> > v2: I've missed that *wnames can also be left uninitialized. Please
> > ignore the patch v1. As an answer to Dominique's comment: my
> > organization marks this statement in all commits.
> >
> > net/9p/protocol.c | 12 +++++-------
> > 1 file changed, 5 insertions(+), 7 deletions(-)
> >
> > diff --git a/net/9p/protocol.c b/net/9p/protocol.c
> > index 4e3a2a1ffcb3..043b621f8b84 100644
> > --- a/net/9p/protocol.c
> > +++ b/net/9p/protocol.c
> > @@ -393,6 +393,8 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
> > case 'T':{
> > uint16_t *nwname = va_arg(ap, uint16_t *);
> > char ***wnames = va_arg(ap, char ***);
> > + int i;
> > + *wnames = NULL;
>
> Consider also initializing `int i = 0;` here. Because ...
>
The hassle with indices in this code can be eliminated with using
kcalloc() instead of kmalloc_array(). It would initialize all the members
to zero and later we can use the fact that kfree() is a no-op for NULL
args and iterate over all the elements - this trick is ubiquitous in
kernel AFAIK.
But when trying to do such kind of changes, I wonder whether it would
impact performance (I'm not able to test this fully) or related issues as
for some reason an unsafe kmalloc_array() was originally used.
If you have no objections, then I'll better prepare a new patch with
this in mind. That will make the code less prone to potential errors in
future.
> >
> > errcode = p9pdu_readf(pdu, proto_version,
> > "w", nwname);
> > @@ -406,8 +408,6 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
> > }
> >
> > if (!errcode) {
> > - int i;
> > -
> > for (i = 0; i < *nwname; i++) {
>
> ... this block that initializes `i` is conditional. I mean it does work right
> now as-is, because ...
>
> > errcode =
> > p9pdu_readf(pdu,
> > @@ -421,13 +421,11 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
> >
> > if (errcode) {
> > if (*wnames) {
> > - int i;
> > -
> > - for (i = 0; i < *nwname; i++)
> > + while (--i >= 0)
> > kfree((*wnames)[i]);
> > + kfree(*wnames);
> > + *wnames = NULL;
> > }
>
> ... this is wrapped into `if (*wnames) {` and you initialized *wnames with
> NULL, but it just feels like a potential future trap somehow.
>
> Anyway, at least it looks like correct behaviour (ATM), so:
>
> Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
>
> > - kfree(*wnames);
> > - *wnames = NULL;
> > }
> > }
> > break;
> >
>
>
next prev parent reply other threads:[~2023-12-05 13:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-05 8:05 [PATCH] net: 9p: avoid freeing uninit memory in p9pdu_vreadf Fedor Pchelkin
2023-12-05 9:07 ` Dominique Martinet
2023-12-05 9:19 ` [PATCH v2] " Fedor Pchelkin
2023-12-05 9:31 ` Dominique Martinet
2023-12-05 12:15 ` Fedor Pchelkin
2023-12-05 12:43 ` Dominique Martinet
2023-12-05 12:29 ` Christian Schoenebeck
2023-12-05 13:09 ` Fedor Pchelkin [this message]
2023-12-05 18:05 ` [PATCH v3] " Fedor Pchelkin
2023-12-06 13:12 ` Christian Schoenebeck
2023-12-06 20:09 ` [PATCH v4] " Fedor Pchelkin
2023-12-07 12:54 ` Christian Schoenebeck
2023-12-11 23:21 ` Dominique Martinet
2024-01-07 7:56 ` Vitaly Chikunov
2024-01-07 9:48 ` Fedor Pchelkin
2024-01-07 10:14 ` Vitaly Chikunov
2024-01-07 10:26 ` Dominique Martinet
2023-12-11 13:51 ` Simon Horman
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