[PATCH] usb: gadget: f_uac1, f_uac2: fix invalid free and memory leak

["syzbot" <syzbot@kernel.org>]

From: Aleksandr Nogikh <nogikh@google.com>

The `UAC1_RATE_ATTRIBUTE` and `UAC2_RATE_ATTRIBUTE` macros generate store
functions that use `strsep()` to parse a comma-separated list of sample
rates. The `strsep()` function modifies the pointer passed to it, advancing
it past the delimiter.

This causes two issues. First, if `kstrtou32()` fails (e.g., due to an
invalid token), the code jumps to the `end` label and calls
`kfree(split_page)`. Since `split_page` has been advanced by `strsep()`,
this results in an invalid free. Second, if the loop completes
successfully, `strsep()` sets `split_page` to `NULL`. The subsequent
`kfree(split_page)` becomes a no-op, leaking the memory allocated by
`kstrdup()`.

KASAN reports the invalid free as follows:

BUG: KASAN: invalid-free in f_uac2_opts_p_srate_store+0x225/0x2b0
drivers/usb/gadget/function/f_uac2.c:2087
Free of addr ffff888192cb7806 by task syz.0.17/6182
Call Trace:
 kfree+0x173/0x6c0 mm/slub.c:6692
 f_uac2_opts_p_srate_store+0x225/0x2b0
 drivers/usb/gadget/function/f_uac2.c:2087
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x33a/0x430 fs/configfs/file.c:229
 vfs_write+0x61e/0xbb0 fs/read_write.c:687
 ksys_write+0x156/0x270 fs/read_write.c:739
The buggy address is located 6 bytes inside of
 32-byte region [ffff888192cb7800, ffff888192cb7820)

Fix this by keeping the original pointer returned by `kstrdup()` in a
separate variable `page_alloc` and passing a temporary pointer `split_page`
to `strsep()`. This ensures that the correct pointer is passed to
`kfree()`. Additionally, add a check to handle `kstrdup()` allocation
failures.

Fixes: a7339e4f5788 ("usb: gadget: f_uac2: Support multiple sampling rates")
Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
Reported-by: syzbot+bfca46c96ddf3b7d5c55@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bfca46c96ddf3b7d5c55
Link: https://syzkaller.appspot.com/ai_job?id=705307cf-805c-4e75-8f76-2a0acc541cb8
Signed-off-by: Aleksandr Nogikh <nogikh@google.com>

---
diff --git a/drivers/usb/gadget/function/f_uac1.c b/drivers/usb/gadget/function/f_uac1.c
index 85c502e98..f4b7bbd93 100644
--- a/drivers/usb/gadget/function/f_uac1.c
+++ b/drivers/usb/gadget/function/f_uac1.c
@@ -1594,6 +1594,7 @@ static ssize_t f_uac1_opts_##name##_store(struct config_item *item,	\
 					  const char *page, size_t len)	\
 {									\
 	struct f_uac1_opts *opts = to_f_uac1_opts(item);		\
+	char *page_alloc = NULL;					\
 	char *split_page = NULL;					\
 	int ret = -EINVAL;						\
 	char *token;							\
@@ -1608,7 +1609,12 @@ static ssize_t f_uac1_opts_##name##_store(struct config_item *item,	\
 									\
 	i = 0;								\
 	memset(opts->name##s, 0x00, sizeof(opts->name##s));		\
-	split_page = kstrdup(page, GFP_KERNEL);				\
+	page_alloc = kstrdup(page, GFP_KERNEL);				\
+	if (!page_alloc) {						\
+		ret = -ENOMEM;						\
+		goto end;						\
+	}								\
+	split_page = page_alloc;					\
 	while ((token = strsep(&split_page, ",")) != NULL) {		\
 		ret = kstrtou32(token, 0, &num);			\
 		if (ret)						\
@@ -1619,7 +1625,7 @@ static ssize_t f_uac1_opts_##name##_store(struct config_item *item,	\
 	};								\
 									\
 end:									\
-	kfree(split_page);						\
+	kfree(page_alloc);						\
 	mutex_unlock(&opts->lock);					\
 	return ret;							\
 }									\
diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index 897787d08..336aeaec9 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -2012,6 +2012,7 @@ static ssize_t f_uac2_opts_##name##_store(struct config_item *item,	\
 					  const char *page, size_t len)	\
 {									\
 	struct f_uac2_opts *opts = to_f_uac2_opts(item);		\
+	char *page_alloc = NULL;					\
 	char *split_page = NULL;					\
 	int ret = -EINVAL;						\
 	char *token;							\
@@ -2026,7 +2027,12 @@ static ssize_t f_uac2_opts_##name##_store(struct config_item *item,	\
 									\
 	i = 0;								\
 	memset(opts->name##s, 0x00, sizeof(opts->name##s));		\
-	split_page = kstrdup(page, GFP_KERNEL);				\
+	page_alloc = kstrdup(page, GFP_KERNEL);				\
+	if (!page_alloc) {						\
+		ret = -ENOMEM;						\
+		goto end;						\
+	}								\
+	split_page = page_alloc;					\
 	while ((token = strsep(&split_page, ",")) != NULL) {		\
 		ret = kstrtou32(token, 0, &num);			\
 		if (ret)						\
@@ -2037,7 +2043,7 @@ static ssize_t f_uac2_opts_##name##_store(struct config_item *item,	\
 	};								\
 									\
 end:									\
-	kfree(split_page);						\
+	kfree(page_alloc);						\
 	mutex_unlock(&opts->lock);					\
 	return ret;							\
 }									\


base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff
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