* Re: [PATCH] usb: gadget: f_uac1_legacy: fix inverted NULL check after kstrndup()
2026-06-25 11:31 [PATCH] usb: gadget: f_uac1_legacy: fix inverted NULL check after kstrndup() Xu Yang
@ 2026-06-25 11:40 ` sashiko-bot
2026-06-25 12:15 ` Frank Li
1 sibling, 0 replies; 3+ messages in thread
From: sashiko-bot @ 2026-06-25 11:40 UTC (permalink / raw)
To: Xu Yang; +Cc: Frank.Li, imx
Thank you for your contribution! Sashiko AI review found 6 potential issue(s) to consider:
Pre-existing issues:
- [High] Missing workqueue cancellation and queue cleanup before freeing `audio` context.
- [High] Unbounded memory leak of `usb_request` objects and buffers upon alternate setting changes.
- [High] Improper handling of `f_audio_buffer_alloc` failure leads to subsequent UAF or ERR_PTR dereference.
- [High] `audio->copy_buf` is not cleared when queued on `alt=0`, causing double list additions.
- [High] The playback workqueue only processes one buffer per run, stranding/leaking buffers.
- [High] A 1-byte out-of-bounds write of a NUL byte occurs in `f_uac1_opts_##name##_show` when reading a string attribute of maximum length.
--
commit 1d07b1a645b0a1199b66ed32d3217e953cef8087
Author: Xu Yang <xu.yang_2@nxp.com>
Date: Thu Jun 25 11:31:54 2026 +0000
usb: gadget: f_uac1_legacy: fix inverted NULL check after kstrndup()
This patch fixes an inverted NULL check on the result of kstrndup() in
f_uac1_opts_##name##_store(). The original code treated a successful
allocation as an error and would return -ENOMEM while proceeding with a
NULL pointer on failure.
> diff --git a/drivers/usb/gadget/function/f_uac1_legacy.c b/drivers/usb/gadget/function/f_uac1_legacy.c
> index 5d201a2e30e7f..e9f2632ce7852 100644
> --- a/drivers/usb/gadget/function/f_uac1_legacy.c
> +++ b/drivers/usb/gadget/function/f_uac1_legacy.c
> @@ -914,7 +914,7 @@ static ssize_t f_uac1_opts_##name##_store(struct config_item *item, \
> goto end; \
> \
> tmp = kstrndup(page, len, GFP_KERNEL); \
> - if (tmp) { \
> + if (!tmp) { \
> ret = -ENOMEM; \
> goto end; \
> } \
[Severity: High]
This is a pre-existing issue, but does f_uac1_opts_##name##_show() have an
out-of-bounds write here?
drivers/usb/gadget/function/f_uac1_legacy.c:UAC1_STR_ATTRIBUTE() {
...
static ssize_t f_uac1_opts_##name##_show(struct config_item *item, \
char *page) \
{ \
...
result = sprintf(page, "%s\n", opts->name); \
...
}
If a user writes an attribute of exactly 4095 bytes, kstrndup stores it with
a length of 4095. During a subsequent read, sprintf() writes the 4095
characters, appends a newline (byte 4096), and then writes the NUL terminator
at index 4096, which overflows the 4096-byte page allocation by 1 byte.
Could this use sysfs_emit() or scnprintf() instead?
[Severity: High]
This is a pre-existing issue, but does f_audio_free() leak resources or cause
a use-after-free?
drivers/usb/gadget/function/f_uac1_legacy.c:f_audio_free() {
...
static void f_audio_free(struct usb_function *f)
{
struct f_audio *audio = func_to_audio(f);
struct f_uac1_legacy_opts *opts;
gaudio_cleanup(&audio->card);
opts = container_of(f->fi, struct f_uac1_legacy_opts, func_inst);
kfree(audio);
...
}
The audio structure is freed without cancelling the asynchronous
audio->playback_work or draining audio->play_queue. If the workqueue is
pending or executing, it will dereference the freed audio object. Any
elements left in the queue are also leaked.
[Severity: High]
This is a pre-existing issue, but does f_audio_set_alt() leak usb_request
objects and buffers?
drivers/usb/gadget/function/f_uac1_legacy.c:f_audio_set_alt() {
...
for (i = 0; i < req_count && err == 0; i++) {
req = usb_ep_alloc_request(out_ep, GFP_ATOMIC);
if (req) {
req->buf = kzalloc(req_buf_size,
GFP_ATOMIC);
...
}
When the interface is set to alt == 1, requests and buffers are dynamically
allocated. However, when the host stops the stream by switching to alt == 0,
these are never freed. Repeated toggling of the alternate setting could
quickly exhaust system memory.
[Severity: High]
This is a pre-existing issue, but does f_audio_out_ep_complete() improperly
handle f_audio_buffer_alloc() failures?
drivers/usb/gadget/function/f_uac1_legacy.c:f_audio_out_ep_complete() {
...
schedule_work(&audio->playback_work);
copy_buf = f_audio_buffer_alloc(audio_buf_size);
if (IS_ERR(copy_buf))
return -ENOMEM;
}
memcpy(copy_buf->buf + copy_buf->actual, req->buf, req->actual);
...
}
If f_audio_buffer_alloc() fails, it returns -ENOMEM immediately, but
audio->copy_buf is left pointing to the old buffer that was just queued for
playback. A subsequent completion would write to this old buffer, potentially
causing a use-after-free.
[Severity: High]
This is a pre-existing issue, but does f_audio_set_alt() incorrectly leave
audio->copy_buf populated when queued?
drivers/usb/gadget/function/f_uac1_legacy.c:f_audio_set_alt() {
...
} else {
struct f_audio_buf *copy_buf = audio->copy_buf;
if (copy_buf) {
list_add_tail(©_buf->list,
&audio->play_queue);
schedule_work(&audio->playback_work);
}
}
...
}
The copy_buf is added to the play_queue, but audio->copy_buf is not cleared.
If the host issues consecutive SET_INTERFACE 0 requests, the driver will
attempt to add the same buffer to the list again, which corrupts the
doubly-linked list.
[Severity: High]
This is a pre-existing issue, but does the playback workqueue strand buffers in
the play queue?
drivers/usb/gadget/function/f_uac1_legacy.c:f_audio_playback_work() {
...
spin_lock_irq(&audio->lock);
if (list_empty(&audio->play_queue)) {
spin_unlock_irq(&audio->lock);
return;
}
play_buf = list_first_entry(&audio->play_queue,
struct f_audio_buf, list);
list_del(&play_buf->list);
spin_unlock_irq(&audio->lock);
...
}
The work item pulls and processes exactly one buffer per execution. If
f_audio_out_ep_complete() adds multiple buffers quickly, schedule_work() may
coalesce the work items. Since there is no while(!list_empty()) loop, any
coalesced buffers are left stranded in the queue, leaking them when the stream
stops.
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260625113154.1954813-1-xu.yang_2@oss.nxp.com?part=1
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] usb: gadget: f_uac1_legacy: fix inverted NULL check after kstrndup()
2026-06-25 11:31 [PATCH] usb: gadget: f_uac1_legacy: fix inverted NULL check after kstrndup() Xu Yang
2026-06-25 11:40 ` sashiko-bot
@ 2026-06-25 12:15 ` Frank Li
1 sibling, 0 replies; 3+ messages in thread
From: Frank Li @ 2026-06-25 12:15 UTC (permalink / raw)
To: Xu Yang
Cc: gregkh, kees, christophe.jaillet, xu.yang_2, hataegu0826, balbi,
andrzej.p, linux-usb, linux-kernel, imx
On Thu, Jun 25, 2026 at 07:31:54PM +0800, Xu Yang wrote:
>
> From: Xu Yang <xu.yang_2@nxp.com>
>
> kstrndup() returns NULL on allocation failure. The condition was
> checking 'if (tmp)' to detect failure, but this is inverted — it
> would treat a successful allocation as an error and return -ENOMEM
> while leaking the string, and proceed with a NULL pointer on failure.
>
> Fix by changing the condition to 'if (!tmp)'.
>
> Fixes: 0854611a19ae ("usb: gadget: f_uac1: add configfs support")
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-sonnet-4-6
> Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> ---
Reviewed-by: Frank Li <Frank.Li@nxp.com>
> drivers/usb/gadget/function/f_uac1_legacy.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/function/f_uac1_legacy.c b/drivers/usb/gadget/function/f_uac1_legacy.c
> index 5d201a2e30e7..e9f2632ce785 100644
> --- a/drivers/usb/gadget/function/f_uac1_legacy.c
> +++ b/drivers/usb/gadget/function/f_uac1_legacy.c
> @@ -914,7 +914,7 @@ static ssize_t f_uac1_opts_##name##_store(struct config_item *item, \
> goto end; \
> \
> tmp = kstrndup(page, len, GFP_KERNEL); \
> - if (tmp) { \
> + if (!tmp) { \
> ret = -ENOMEM; \
> goto end; \
> } \
> --
> 2.34.1
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread