linux-kernel - [PATCH] fs/coda: Do not use partially allocated struct

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Date:   Fri, 20 May 2022 09:59:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jan Harkes <jaharkes@...cmu.edu>
Cc:     Kees Cook <keescook@...omium.org>, coda@...cmu.edu,
        codalist@...a.cs.cmu.edu, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] fs/coda: Do not use partially allocated struct

GCC 12 does not like seeing a partially allocated structure being used,
especially when a pointer is being passed out of function scope. Since
only the struct coda_in_hdr member of union inputArgs is being allocated
and used, just replace union inputArgs with struct coda_in_hdr.

../fs/coda/upcall.c: In function 'coda_upcall':
../fs/coda/upcall.c:801:22: warning: array subscript 'union inputArgs[0]' is partly outside array bounds of 'unsigned char[20]' [-Warray-bounds]
  801 |         sig_inputArgs->ih.opcode = CODA_SIGNAL;
      |                      ^~
In file included from ../include/linux/fs.h:45,
                 from ../include/linux/huge_mm.h:8,
                 from ../include/linux/mm.h:700,
                 from ../fs/coda/upcall.c:22:
In function 'kvmalloc',
    inlined from 'kvzalloc' at ../include/linux/slab.h:758:9,
    inlined from 'coda_upcall' at ../fs/coda/upcall.c:794:18:
../include/linux/slab.h:750:16: note: object of size 20 allocated by 'kvmalloc_node'
  750 |         return kvmalloc_node(size, flags, NUMA_NO_NODE);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../fs/coda/upcall.c: In function 'coda_upcall':
../fs/coda/upcall.c:802:22: warning: array subscript 'union inputArgs[0]' is partly outside array bounds of 'unsigned char[20]' [-Warray-bounds]
  802 |         sig_inputArgs->ih.unique = req->uc_unique;
      |                      ^~
In function 'kvmalloc',
    inlined from 'kvzalloc' at ../include/linux/slab.h:758:9,
    inlined from 'coda_upcall' at ../fs/coda/upcall.c:794:18:
../include/linux/slab.h:750:16: note: object of size 20 allocated by 'kvmalloc_node'
  750 |         return kvmalloc_node(size, flags, NUMA_NO_NODE);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Jan Harkes <jaharkes@...cmu.edu>
Cc: coda@...cmu.edu
Cc: codalist@...a.cs.cmu.edu
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/coda/upcall.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/coda/upcall.c b/fs/coda/upcall.c
index 59f6cfd06f96..21e4f5f446b2 100644
--- a/fs/coda/upcall.c
+++ b/fs/coda/upcall.c
@@ -711,7 +711,7 @@ static int coda_upcall(struct venus_comm *vcp,
 		       union inputArgs *buffer)
 {
 	union outputArgs *out;
-	union inputArgs *sig_inputArgs;
+	struct coda_in_hdr *ih;
 	struct upc_req *req = NULL, *sig_req;
 	int error;
 
@@ -791,22 +791,22 @@ static int coda_upcall(struct venus_comm *vcp,
 	sig_req = kmalloc(sizeof(struct upc_req), GFP_KERNEL);
 	if (!sig_req) goto exit;
 
-	sig_inputArgs = kvzalloc(sizeof(struct coda_in_hdr), GFP_KERNEL);
-	if (!sig_inputArgs) {
+	ih = kvzalloc(sizeof(*ih), GFP_KERNEL);
+	if (!ih) {
 		kfree(sig_req);
 		goto exit;
 	}
 
 	error = -EINTR;
-	sig_inputArgs->ih.opcode = CODA_SIGNAL;
-	sig_inputArgs->ih.unique = req->uc_unique;
+	ih->opcode = CODA_SIGNAL;
+	ih->unique = req->uc_unique;
 
 	sig_req->uc_flags = CODA_REQ_ASYNC;
-	sig_req->uc_opcode = sig_inputArgs->ih.opcode;
-	sig_req->uc_unique = sig_inputArgs->ih.unique;
-	sig_req->uc_data = (void *)sig_inputArgs;
-	sig_req->uc_inSize = sizeof(struct coda_in_hdr);
-	sig_req->uc_outSize = sizeof(struct coda_in_hdr);
+	sig_req->uc_opcode = ih->opcode;
+	sig_req->uc_unique = ih->unique;
+	sig_req->uc_data = (void *)ih;
+	sig_req->uc_inSize = sizeof(*ih);
+	sig_req->uc_outSize = sizeof(*ih);
 
 	/* insert at head of queue! */
 	list_add(&(sig_req->uc_chain), &vcp->vc_pending);
-- 
2.32.0