[syzbot] [usb?] memory leak in uvcg_extension_ba_source_id_store

[syzbot] [usb?] memory leak in uvcg_extension_ba_source_id_store

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    11028ab62899 Merge tag 'probes-fixes-v7.2-rc5' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13b5b03e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ba7c2d1679fb08a2
dashboard link: https://syzkaller.appspot.com/bug?extid=54927260acba030187a6
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12985499580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16ab649e580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b677b453b580/disk-11028ab6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/eec6e520d498/vmlinux-11028ab6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/03c59bb4309c/bzImage-11028ab6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+54927260acba030187a6@syzkaller.appspotmail.com

BUG: memory leak
unreferenced object 0xffff88810ddbd588 (size 8):
  comm "syz.1.37", pid 6113, jiffies 4294948281
  hex dump (first 8 bytes):
    01 00 00 00 00 00 00 00                          ........
  backtrace (crc ccaa009e):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4597 [inline]
    slab_alloc_node mm/slub.c:4917 [inline]
    __do_kmalloc_node mm/slub.c:5333 [inline]
    __kmalloc_noprof+0x3bf/0x550 mm/slub.c:5359
    _kmalloc_noprof include/linux/slab.h:992 [inline]
    _kmalloc_array_noprof include/linux/slab.h:1208 [inline]
    uvcg_extension_ba_source_id_store+0xee/0x180 drivers/usb/gadget/function/uvc_configfs.c:1058
    flush_write_buffer fs/configfs/file.c:207 [inline]
    configfs_write_iter+0x10d/0x1a0 fs/configfs/file.c:229
    new_sync_write fs/read_write.c:595 [inline]
    vfs_write+0x3ac/0x720 fs/read_write.c:687
    ksys_write+0xa5/0x170 fs/read_write.c:739
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xf8/0x610 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF


---
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Forwarded: #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 11028ab62899

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***

Subject: #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 11028ab62899
Author: rwarwatkar@gmail.com

From a6329c2864899c7c7ac2c20b9d3e04bf598c6870 Mon Sep 17 00:00:00 2001
From: Rituparna Warwatkar <rwarwatkar@gmail.com>
Date: Sat, 1 Aug 2026 03:31:03 +0000
Subject: [PATCH] usb: gadget: uvc: don't pack struct
 uvcg_extension_unit_descriptor

kmemleak reports the baSourceID and bmControls arrays allocated by the
UVC extension-unit configfs attributes as leaked, e.g.:

  BUG: memory leak
  unreferenced object 0xffff888114fee2c0 (size 8):
    __kmalloc_noprof
    uvcg_extension_ba_source_id_store
    configfs_write_iter
    vfs_write
    ksys_write

The arrays are not actually leaked: they are reachable through
xu->desc.baSourceID / xu->desc.bmControls and are freed when the
extension unit is removed.  The problem is that struct
uvcg_extension_unit_descriptor is marked __packed, so these two heap
pointers are stored at unaligned offsets (22 and 31).  kmemleak only
scans memory on pointer-aligned boundaries, so it never sees the
pointers and reports the arrays as unreferenced.

Unlike the UAPI struct uvc_extension_unit_descriptor, this is a purely
in-memory staging structure: baSourceID and bmControls are pointers,
not inline arrays, and the wire descriptor is assembled field by field
in UVC_COPY_XU_DESCRIPTOR().  Nothing relies on the packed layout, so
the __packed attribute is unnecessary and only serves to misalign the
pointers.

Drop __packed so the pointers are naturally aligned and visible to
kmemleak, silencing the false positive.

Fixes: 0525210c9840 ("usb: gadget: uvc: Allow definition of XUs in configfs")
Reported-by: syzbot+54927260acba030187a6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=54927260acba030187a6
Signed-off-by: Rituparna Warwatkar <rwarwatkar@gmail.com>
---
 drivers/usb/gadget/function/uvc_configfs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/uvc_configfs.h b/drivers/usb/gadget/function/uvc_configfs.h
index 9391614135e..5a882afbce4 100644
--- a/drivers/usb/gadget/function/uvc_configfs.h
+++ b/drivers/usb/gadget/function/uvc_configfs.h
@@ -176,7 +176,7 @@ struct uvcg_extension_unit_descriptor {
        u8 bControlSize;
        u8 *bmControls;
        u8 iExtension;
-} __packed;
+};

 struct uvcg_extension {
        struct config_item item;
--
2.47.3

Forwarded: #syz test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: #syz test
Author: rwarwatkar@gmail.com

From a6329c2864899c7c7ac2c20b9d3e04bf598c6870 Mon Sep 17 00:00:00 2001
From: Rituparna Warwatkar <rwarwatkar@gmail.com>
Date: Sat, 1 Aug 2026 03:31:03 +0000
Subject: [PATCH] usb: gadget: uvc: don't pack struct
 uvcg_extension_unit_descriptor

kmemleak reports the baSourceID and bmControls arrays allocated by the
UVC extension-unit configfs attributes as leaked, e.g.:

  BUG: memory leak
  unreferenced object 0xffff888114fee2c0 (size 8):
    __kmalloc_noprof
    uvcg_extension_ba_source_id_store
    configfs_write_iter
    vfs_write
    ksys_write

The arrays are not actually leaked: they are reachable through
xu->desc.baSourceID / xu->desc.bmControls and are freed when the
extension unit is removed.  The problem is that struct
uvcg_extension_unit_descriptor is marked __packed, so these two heap
pointers are stored at unaligned offsets (22 and 31).  kmemleak only
scans memory on pointer-aligned boundaries, so it never sees the
pointers and reports the arrays as unreferenced.

Unlike the UAPI struct uvc_extension_unit_descriptor, this is a purely
in-memory staging structure: baSourceID and bmControls are pointers,
not inline arrays, and the wire descriptor is assembled field by field
in UVC_COPY_XU_DESCRIPTOR().  Nothing relies on the packed layout, so
the __packed attribute is unnecessary and only serves to misalign the
pointers.

Drop __packed so the pointers are naturally aligned and visible to
kmemleak, silencing the false positive.

Fixes: 0525210c9840 ("usb: gadget: uvc: Allow definition of XUs in configfs")
Reported-by: syzbot+54927260acba030187a6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=54927260acba030187a6
Signed-off-by: Rituparna Warwatkar <rwarwatkar@gmail.com>
---
 drivers/usb/gadget/function/uvc_configfs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/uvc_configfs.h b/drivers/usb/gadget/function/uvc_configfs.h
index 9391614135e..5a882afbce4 100644
--- a/drivers/usb/gadget/function/uvc_configfs.h
+++ b/drivers/usb/gadget/function/uvc_configfs.h
@@ -176,7 +176,7 @@ struct uvcg_extension_unit_descriptor {
        u8 bControlSize;
        u8 *bmControls;
        u8 iExtension;
-} __packed;
+};

 struct uvcg_extension {
        struct config_item item;
--
2.47.3