[PATCH 5.18 853/879] misc: fastrpc: fix list iterator in fastrpc_req_mem_unmap_impl

Greg Kroah-Hartman
2022-06-08T03:18:00Z

From: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>

commit c5c07c5958cf0c9af6e76813e6de15d42ee49822 upstream.

This is another instance of incorrect use of list iterator and
checking it for NULL.

The list iterator value 'map' will *always* be set and non-NULL
by list_for_each_entry(), so it is incorrect to assume that the
iterator value will be NULL if the list is empty (in this case, the
check 'if (!map) {' will always be false and never exit as expected).

To fix the bug, use a new variable 'iter' as the list iterator,
while use the original variable 'map' as a dedicated pointer to
point to the found element.

Without this patch, Kernel crashes with below trace:

Unable to handle kernel access to user memory outside uaccess routines
at virtual address 0000ffff7fb03750
...
Call trace:
fastrpc_map_create+0x70/0x290 [fastrpc]
fastrpc_req_mem_map+0xf0/0x2dc [fastrpc]
fastrpc_device_ioctl+0x138/0xc60 [fastrpc]
__arm64_sys_ioctl+0xa8/0xec
invoke_syscall+0x48/0x114
el0_svc_common.constprop.0+0xd4/0xfc
do_el0_svc+0x28/0x90
el0_svc+0x3c/0x130
el0t_64_sync_handler+0xa4/0x130
el0t_64_sync+0x18c/0x190
Code: 14000016 f94000a5 eb05029f 54000260 (b94018a6)
---[ end trace 0000000000000000 ]---

Fixes: 5c1b97c7d7b7 ("misc: fastrpc: add support for FASTRPC_IOCTL_MEM_MAP/UNMAP")
Cc: stable@vger.kernel.org
Reported-by: Jan Jablonsky <jjablonsky@snapchat.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20220518152353.13058-1-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/misc/fastrpc.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1747,17 +1747,18 @@ err_invoke:
static int fastrpc_req_mem_unmap_impl(struct fastrpc_user *fl, struct fastrpc_mem_unmap *req)
{
struct fastrpc_invoke_args args[1] = { [0] = { 0 } };
- struct fastrpc_map *map = NULL, *m;
+ struct fastrpc_map *map = NULL, *iter, *m;
struct fastrpc_mem_unmap_req_msg req_msg = { 0 };
int err = 0;
u32 sc;
struct device *dev = fl->sctx->dev;

spin_lock(&fl->lock);
- list_for_each_entry_safe(map, m, &fl->maps, node) {
- if ((req->fd < 0 || map->fd == req->fd) && (map->raddr == req->vaddr))
+ list_for_each_entry_safe(iter, m, &fl->maps, node) {
+ if ((req->fd < 0 || iter->fd == req->fd) && (iter->raddr == req->vaddr)) {
+ map = iter;
break;
- map = NULL;
+ }
}

spin_unlock(&fl->lock);