[dm-devel] [PATCH] libmultipath: fix null dereference in add

[Benjamin Marzinski]

On Mon, Aug 03, 2020 at 07:57:01PM +0800, lixiaokeng wrote:
> I got a multipath segfault while running iscsi login/logout and following scripts in parallel:
> 
> #!/bin/bash
> interval=1
> while true
> do
>               multipath -F &> /dev/null
>               multipath -r &> /dev/null
>               multipath -v2 &> /dev/null
>               multipath -ll &> /dev/null
>               sleep $interval
> done
> 
> This is the debuginfo:
> #0  0x00007f3805e4df58 in add (ctx=0x55d1569e4a00, ud=0x55d1569bafd0) at nvme.c:801
> 801              if (strcmp("disk", udev_device_get_devtype(ud)))
> (gdb) bt
> #0  0x00007f3805e4df58 in add (ctx=0x55d1569e4a00, ud=0x55d1569bafd0) at nvme.c:801
> #1  0x00007f3806687a44 in add_foreign (udev=0x55d1569bafd0) at foreign.c:299
> #2  0x00007f3806665abf in is_claimed_by_foreign (ud=<optimized out>) at foreign.h:316
> #3  pathinfo (pp=0x55d1569e9f50, conf=0x55d1569b92d0, mask=69) at discovery.c:2064
> #4  0x000055d154c91cbb in check_usable_paths (conf=0x55d1569b92d0, devpath=0x55d1569e3200 "dm-6", dev_type=<optimized out>) at main.c:368
> #5  0x000055d154c910a5 in main (argc=3, argv=<optimized out>) at main.c:1057
> In add() at libmultipath/foreign/nvme.c, udev_device_get_devtype(ud) return a NULL pointer then dereferenced.
> Here, NULL check is needed.
> Check if udev_device_get_devtype return NULL before dereferencing it.

This patch looks fine. However, it has pointed out a larger problem with
the udev_device_get_* functions. This is not the only instance where we
aren't checking the return value of these functions before dereferencing
it.

-Ben

Reviewed-by: Benjamin Marzinski <bmarzins at redhat.coM>
 
> Signed-off-by: lutianxiong <lutianxiong huawei com>
> Signed-off-by: lixiaokeng <lixiaokeng at huawei.com>
> ---
>  libmultipath/foreign/nvme.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/libmultipath/foreign/nvme.c b/libmultipath/foreign/nvme.c
> index 280b6bd..6061999 100644
> --- a/libmultipath/foreign/nvme.c
> +++ b/libmultipath/foreign/nvme.c
> @@ -600,12 +600,14 @@ int add(struct context *ctx, struct udev_device *ud)
>  {
>  	struct udev_device *subsys;
>  	int rc;
> +	const char *devtype;
> 
>  	condlog(5, "%s called for \"%s\"", __func__, THIS);
> 
>  	if (ud == NULL)
>  		return FOREIGN_ERR;
> -	if (strcmp("disk", udev_device_get_devtype(ud)))
> +	if ((devtype = udev_device_get_devtype(ud)) == NULL ||
> +						strcmp("disk", devtype))
>  		return FOREIGN_IGNORED;
> 
>  	subsys = udev_device_get_parent_with_subsystem_devtype(ud,
> --