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SubjectRe: [patch -target tree] usb: gadget: f_tcm: use after free
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Hi Andrzej,

On Wed, 2016-03-09 at 13:53 +0100, Andrzej Pietrasiewicz wrote:
> Hi Nicholas,
>
> W dniu 05.03.2016 o 08:26, Nicholas A. Bellinger pisze:
> > Hi Felipe + usb-gadget folks,
> >
> > On Wed, 2016-03-02 at 13:55 +0200, Felipe Balbi wrote:
>
> <snip>
>
> >
> > usb-gadget/tcm: Conversion to percpu_ida tag pre-allocation
> > http://www.spinics.net/lists/target-devel/msg11777.html
> >
> > usb-gadget/tcm: Convert to TARGET_SCF_ACK_KREF I/O krefs
> > http://www.spinics.net/lists/target-devel/msg11782.html
> >
> > Felipe, Sebastian, & Andrezj, would you be so kind to review and test
> > usb-gadget using target-pending/for-next code..?
> >
> >
>
> Actually I have noticed a problem at
> 8b00965 "target: Convert demo-mode only drivers to target_alloc_session"
>
> I get:
>
> [ 1698.406304] configfs-gadget gadget: high-speed config #1: c
> [ 1698.410547] Using the BOT protocol
> [ 1698.414163] Missing nexus, ignoring command
> [ 1698.417944] bot_cmd_complete(309): -22
>
> I think the third message is from f_tcm. It is because
> tpg->tpg_nexus is not set anymore, because the line
>
> tpg->tpg_nexus = tv_nexus;
>
> is removed by the commit mentioned above.
>
> Restoring this line fixes the problem.

Thanks for testing!

Applying the following patch to re-add the missing assingment
as a proper alloc_session callback.

diff --git a/drivers/usb/gadget/function/f_tcm.c b/drivers/usb/gadget/function/f_tcm.c
index e352a31..348140c 100644
--- a/drivers/usb/gadget/function/f_tcm.c
+++ b/drivers/usb/gadget/function/f_tcm.c
@@ -1570,6 +1570,16 @@ out:
return ret;
}

+static int usbg_alloc_sess_cb(struct se_portal_group *se_tpg,
+ struct se_session *se_sess, void *p)
+{
+ struct usbg_tpg *tpg = container_of(se_tpg,
+ struct usbg_tpg, se_tpg);
+
+ tpg->tpg_nexus = p;
+ return 0;
+}
+
static int tcm_usbg_make_nexus(struct usbg_tpg *tpg, char *name)
{
struct tcm_usbg_nexus *tv_nexus;
@@ -1591,7 +1601,7 @@ static int tcm_usbg_make_nexus(struct usbg_tpg *tpg, char *name)
tv_nexus->tvn_se_sess = target_alloc_session(&tpg->se_tpg, 128,
sizeof(struct usbg_cmd),
TARGET_PROT_NORMAL, name,
- tv_nexus, NULL);
+ tv_nexus, usbg_alloc_sess_cb);
if (IS_ERR(tv_nexus->tvn_se_sess)) {
#define MAKE_NEXUS_MSG "core_tpg_check_initiator_node_acl() failed for %s\n"
pr_debug(MAKE_NEXUS_MSG, name);
>
> Then percpu_ida commit produces the below result
> (it does not happen immediately, but a while after
> running the script).
> I did not bisect, though; I only checked the commits
> which alter drivers/usb/gadget/function/f_tcm.c.
> The last one which (almost) works is:
>
> 8b00965 "target: Convert demo-mode only drivers to target_alloc_session"
>
> AP
>
> I used the following script:
>
> 8<----------------------------
>
> #!/bin/bash
>
> mount -t configfs none /sys/kernel/config
> modprobe libcomposite
> cd /sys/kernel/config/usb_gadget
> mkdir tcm
> cd tcm
> mkdir functions/tcm.0
> cd /sys/kernel/config/target/
> mkdir usb_gadget
> cd usb_gadget
> mkdir naa.0123456789abcdef
> cd naa.0123456789abcdef
> mkdir tpgt_1
> cd tpgt_1
> echo naa.01234567890abcdef > nexus
> echo 1 > enable
> cd /sys/kernel/config/usb_gadget/tcm
> mkdir configs/c.1
> ln -s functions/tcm.0 configs/c.1
> echo 0x0525 > idVendor
> echo 0x1234 > idProduct
> echo 12400000.dwc3 > UDC
>
> 8<----------------------------
>
> # [ 45.510513] ERR bot_status_complete(73)
> [ 45.671921] configfs-gadget gadget: high-speed config #1: c
> [ 45.676158] Using the BOT protocol
> [ 45.679860] ------------[ cut here ]------------
> [ 45.683981] kernel BUG at drivers/target/target_core_transport.c:1476!

Mmmm, usbg_get_cmd() was missing an explicit memset() after tag lookup.

How about the following..?

diff --git a/drivers/usb/gadget/function/f_tcm.c b/drivers/usb/gadget/function/f_tcm.c
index e352a31..d4e8a91 100644
--- a/drivers/usb/gadget/function/f_tcm.c
+++ b/drivers/usb/gadget/function/f_tcm.c
@@ -1078,6 +1078,7 @@ static struct usbg_cmd *usbg_get_cmd(struct f_uas *fu,
return ERR_PTR(-ENOMEM);

cmd = &((struct usbg_cmd *)se_sess->sess_cmd_map)[tag];
+ memset(cmd, 0, sizeof(*cmd));
cmd->se_cmd.map_tag = tag;
cmd->se_cmd.tag = cmd->tag = scsi_tag;
cmd->fu = fu;
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