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authorAlan Stern <stern@rowland.harvard.edu>2022-12-23 09:59:09 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2023-01-17 16:36:15 +0100
commitd18dcfe9860e842f394e37ba01ca9440ab2178f4 (patch)
tree946bb355c8372c77641fada77ad5e70df6f3017c /drivers/usb
parent1301c7b9f7efad2f11ef924e317c18ebd714fc9a (diff)
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=C6d04DjzA9ffa5x1g@mail.gmail.com/ 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>
Diffstat (limited to 'drivers/usb')
-rw-r--r--drivers/usb/gadget/legacy/inode.c28
1 files 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);
}
/*----------------------------------------------------------------------*/