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net/9p/usbg: fix prefix matching in device lookup

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p9_usbg_create() matches the mount source against registered usb9pfs
instance tags with strncmp() and the length of the caller supplied source.
That accepts any prefix of the registered tag.

For example, a gadget instance tagged "secret_channel" can be selected with
"s", "sec", or any other non-empty prefix.  Once selected, the instance is
marked in use and the client is attached to that transport.  This differs
from the configfs tag lookup path, which uses strcmp() and therefore
requires an exact tag match.

Require an exact tag match in p9_usbg_create() as well.

Fixes: a3be076dc1 ("net/9p/usbg: Add new usb gadget function transport")
Cc: stable@vger.kernel.org
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: GLM:GLM-5.1
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Co-developed-by: Jackie Liu <liuyun01@kylinos.cn>
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Message-ID: <20260607121907.12588-1-zhaoyz24@mails.tsinghua.edu.cn>
Message-ID: <20260719040346.88295-1-liu.yun@linux.dev>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
This commit is contained in:
Yizhou Zhao 2026-06-07 20:19:04 +08:00 committed by Dominique Martinet
parent 0955472fff
commit 9ee83ef8d2
1 changed files with 1 additions and 1 deletions
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2
net/9p/trans_usbg.c
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@ -391,7 +391,7 @@ static int p9_usbg_create(struct p9_client *client, struct fs_context *fc)
guard(mutex)(&usb9pfs_lock);
list_for_each_entry(dev, &usbg_instance_list, usb9pfs_instance) {
if (!strncmp(devname, dev->tag, strlen(devname))) {
if (!strcmp(devname, dev->tag)) {
if (!dev->inuse) {
dev->inuse = true;
found = 1;