This is a note to let you know that I've just added the patch titled
USB: gadgetfs: Fix race between mounting and unmounting
to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From d18dcfe9860e842f394e37ba01ca9440ab2178f4 Mon Sep 17 00:00:00 2001 From: Alan Stern stern@rowland.harvard.edu Date: Fri, 23 Dec 2022 09:59:09 -0500 Subject: USB: gadgetfs: Fix race between mounting and unmounting
The syzbot fuzzer and Gerald Lee have identified a use-after-free bug in the gadgetfs driver, involving processes concurrently mounting and unmounting the gadgetfs filesystem. In particular, gadgetfs_fill_super() can race with gadgetfs_kill_sb(), causing the latter to deallocate the_device while the former is using it. The output from KASAN says, in part:
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:102 [inline] BUG: KASAN: use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:176 [inline] BUG: KASAN: use-after-free in __refcount_sub_and_test include/linux/refcount.h:272 [inline] BUG: KASAN: use-after-free in __refcount_dec_and_test include/linux/refcount.h:315 [inline] BUG: KASAN: use-after-free in refcount_dec_and_test include/linux/refcount.h:333 [inline] BUG: KASAN: use-after-free in put_dev drivers/usb/gadget/legacy/inode.c:159 [inline] BUG: KASAN: use-after-free in gadgetfs_kill_sb+0x33/0x100 drivers/usb/gadget/legacy/inode.c:2086 Write of size 4 at addr ffff8880276d7840 by task syz-executor126/18689
CPU: 0 PID: 18689 Comm: syz-executor126 Not tainted 6.1.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022 Call Trace: <TASK> ... atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:176 [inline] __refcount_sub_and_test include/linux/refcount.h:272 [inline] __refcount_dec_and_test include/linux/refcount.h:315 [inline] refcount_dec_and_test include/linux/refcount.h:333 [inline] put_dev drivers/usb/gadget/legacy/inode.c:159 [inline] gadgetfs_kill_sb+0x33/0x100 drivers/usb/gadget/legacy/inode.c:2086 deactivate_locked_super+0xa7/0xf0 fs/super.c:332 vfs_get_super fs/super.c:1190 [inline] get_tree_single+0xd0/0x160 fs/super.c:1207 vfs_get_tree+0x88/0x270 fs/super.c:1531 vfs_fsconfig_locked fs/fsopen.c:232 [inline]
The simplest solution is to ensure that gadgetfs_fill_super() and gadgetfs_kill_sb() are serialized by making them both acquire a new mutex.
Signed-off-by: Alan Stern stern@rowland.harvard.edu Reported-and-tested-by: syzbot+33d7ad66d65044b93f16@syzkaller.appspotmail.com Reported-and-tested-by: Gerald Lee sundaywind2004@gmail.com Link: https://lore.kernel.org/linux-usb/CAO3qeMVzXDP-JU6v1u5Ags6Q-bb35kg3=C6d04Djz... Fixes: e5d82a7360d1 ("vfs: Convert gadgetfs to use the new mount API") CC: stable@vger.kernel.org Link: https://lore.kernel.org/r/Y6XCPXBpn3tmjdCC@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/gadget/legacy/inode.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-)
diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c index 01c3ead7d1b4..d605bc2e7e8f 100644 --- a/drivers/usb/gadget/legacy/inode.c +++ b/drivers/usb/gadget/legacy/inode.c @@ -229,6 +229,7 @@ static void put_ep (struct ep_data *data) */
static const char *CHIP; +static DEFINE_MUTEX(sb_mutex); /* Serialize superblock operations */
/*----------------------------------------------------------------------*/
@@ -2010,13 +2011,20 @@ gadgetfs_fill_super (struct super_block *sb, struct fs_context *fc) { struct inode *inode; struct dev_data *dev; + int rc;
- if (the_device) - return -ESRCH; + mutex_lock(&sb_mutex); + + if (the_device) { + rc = -ESRCH; + goto Done; + }
CHIP = usb_get_gadget_udc_name(); - if (!CHIP) - return -ENODEV; + if (!CHIP) { + rc = -ENODEV; + goto Done; + }
/* superblock */ sb->s_blocksize = PAGE_SIZE; @@ -2053,13 +2061,17 @@ gadgetfs_fill_super (struct super_block *sb, struct fs_context *fc) * from binding to a controller. */ the_device = dev; - return 0; + rc = 0; + goto Done;
-Enomem: + Enomem: kfree(CHIP); CHIP = NULL; + rc = -ENOMEM;
- return -ENOMEM; + Done: + mutex_unlock(&sb_mutex); + return rc; }
/* "mount -t gadgetfs path /dev/gadget" ends up here */ @@ -2081,6 +2093,7 @@ static int gadgetfs_init_fs_context(struct fs_context *fc) static void gadgetfs_kill_sb (struct super_block *sb) { + mutex_lock(&sb_mutex); kill_litter_super (sb); if (the_device) { put_dev (the_device); @@ -2088,6 +2101,7 @@ gadgetfs_kill_sb (struct super_block *sb) } kfree(CHIP); CHIP = NULL; + mutex_unlock(&sb_mutex); }
/*----------------------------------------------------------------------*/