[PATCH 4.19 08/97] thunderbolt: Prevent crash if non-active NVMem file is read

Greg Kroah-Hartman
2020-02-27T14:03:28Z

From: Mika Westerberg <mika.westerberg@linux.intel.com>

commit 03cd45d2e219301880cabc357e3cf478a500080f upstream.

The driver does not populate .reg_read callback for the non-active NVMem
because the file is supposed to be write-only. However, it turns out
NVMem subsystem does not yet support this and expects that the .reg_read
callback is provided. If user reads the binary attribute it triggers
NULL pointer dereference like this one:

BUG: kernel NULL pointer dereference, address: 0000000000000000
...
Call Trace:
bin_attr_nvmem_read+0x64/0x80
kernfs_fop_read+0xa7/0x180
vfs_read+0xbd/0x170
ksys_read+0x5a/0xd0
do_syscall_64+0x43/0x150
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fix this in the driver by providing .reg_read callback that always
returns an error.

Reported-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Fixes: e6b245ccd524 ("thunderbolt: Add support for host and device NVM firmware upgrade")
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200213095604.1074-1-mika.westerberg@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/thunderbolt/switch.c | 7 +++++++
1 file changed, 7 insertions(+)

--- a/drivers/thunderbolt/switch.c
+++ b/drivers/thunderbolt/switch.c
@@ -264,6 +264,12 @@ static int tb_switch_nvm_read(void *priv
return ret;
}

+static int tb_switch_nvm_no_read(void *priv, unsigned int offset, void *val,
+ size_t bytes)
+{
+ return -EPERM;
+}
+
static int tb_switch_nvm_write(void *priv, unsigned int offset, void *val,
size_t bytes)
{
@@ -309,6 +315,7 @@ static struct nvmem_device *register_nvm
config.read_only = true;
} else {
config.name = "nvm_non_active";
+ config.reg_read = tb_switch_nvm_no_read;
config.reg_write = tb_switch_nvm_write;
config.root_only = true;
}