CVE-2022-33981 (published 2022-06-18T16:15Z)

drivers/block/floppy.c in the Linux kernel before 5.17.6 is vulnerable to a denial of service, because of a concurrency use-after-free flaw after deallocating raw_cmd in the raw_cmd_ioctl function.

Severity: LOW
CVSS v2 base score: 2.1 (AV:L/AC:L/Au:N/C:N/I:N/A:P)
CVSS v3 base score: 3.3, LOW (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L)

Weakness information:
cwe_id: CWE-416
cwe_name: Use After Free
description: The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
extended_description: 
             
             
             
			 
             
             
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Willy Tarreau
author_date: 2022-04-26 23:41:05+03:00
msg: floppy: disable FDRAWCMD by default

Minh Yuan reported a concurrency use-after-free issue in the floppy code
between raw_cmd_ioctl and seek_interrupt.

[ It turns out this has been around, and that others have reported the
  KASAN splats over the years, but Minh Yuan had a reproducer for it and
  so gets primary credit for reporting it for this fix   - Linus ]

The problem is, this driver tends to break very easily and nowadays,
nobody is expected to use FDRAWCMD anyway since it was used to
manipulate non-standard formats.  The risk of breaking the driver is
higher than the risk presented by this race, and accessing the device
requires privileges anyway.

Let's just add a config option to completely disable this ioctl and
leave it disabled by default.  Distros shouldn't use it, and only those
running on antique hardware might need to enable it.

Link: https://lore.kernel.org/all/000000000000b71cdd05d703f6bf@google.com/
Link: https://lore.kernel.org/lkml/CAKcFiNC=MfYVW-Jt9A3=FPJpTwCD2PL_ULNCpsCVE5s8ZeBQgQ@mail.gmail.com
Link: https://lore.kernel.org/all/CAEAjamu1FRhz6StCe_55XY5s389ZP_xmCF69k987En+1z53=eg@mail.gmail.com
Reported-by: Minh Yuan <yuanmingbuaa@gmail.com>
Reported-by: syzbot+8e8958586909d62b6840@syzkaller.appspotmail.com
Reported-by: cruise k <cruise4k@gmail.com>
Reported-by: Kyungtae Kim <kt0755@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Tested-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: Kconfig
change_type: ModificationType.MODIFY
diff: @@ -33,6 +33,22 @@ config BLK_DEV_FD
 	  To compile this driver as a module, choose M here: the
 	  module will be called floppy.
 
+config BLK_DEV_FD_RAWCMD
+	bool "Support for raw floppy disk commands (DEPRECATED)"
+	depends on BLK_DEV_FD
+	help
+	  If you want to use actual physical floppies and expect to do
+	  special low-level hardware accesses to them (access and use
+	  non-standard formats, for example), then enable this.
+
+	  Note that the code enabled by this option is rarely used and
+	  might be unstable or insecure, and distros should not enable it.
+
+	  Note: FDRAWCMD is deprecated and will be removed from the kernel
+	  in the near future.
+
+	  If unsure, say N.
+
 config AMIGA_FLOPPY
 	tristate "Amiga floppy support"
 	depends on AMIGA

programming_language: Go
filename: floppy.c
change_type: ModificationType.MODIFY
diff: @@ -2982,6 +2982,8 @@ static const char *drive_name(int type, int drive)
 		return "(null)";
 }
 
+#ifdef CONFIG_BLK_DEV_FD_RAWCMD
+
 /* raw commands */
 static void raw_cmd_done(int flag)
 {
@@ -3181,6 +3183,35 @@ static int raw_cmd_ioctl(int cmd, void __user *param)
 	return ret;
 }
 
+static int floppy_raw_cmd_ioctl(int type, int drive, int cmd,
+				void __user *param)
+{
+	int ret;
+
+	pr_warn_once("Note: FDRAWCMD is deprecated and will be removed from the kernel in the near future.\n");
+
+	if (type)
+		return -EINVAL;
+	if (lock_fdc(drive))
+		return -EINTR;
+	set_floppy(drive);
+	ret = raw_cmd_ioctl(cmd, param);
+	if (ret == -EINTR)
+		return -EINTR;
+	process_fd_request();
+	return ret;
+}
+
+#else /* CONFIG_BLK_DEV_FD_RAWCMD */
+
+static int floppy_raw_cmd_ioctl(int type, int drive, int cmd,
+				void __user *param)
+{
+	return -EOPNOTSUPP;
+}
+
+#endif
+
 static int invalidate_drive(struct block_device *bdev)
 {
 	/* invalidate the buffer track to force a reread */
@@ -3369,7 +3400,6 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
 {
 	int drive = (long)bdev->bd_disk->private_data;
 	int type = ITYPE(drive_state[drive].fd_device);
-	int i;
 	int ret;
 	int size;
 	union inparam {
@@ -3520,16 +3550,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
 		outparam = &write_errors[drive];
 		break;
 	case FDRAWCMD:
-		if (type)
-			return -EINVAL;
-		if (lock_fdc(drive))
-			return -EINTR;
-		set_floppy(drive);
-		i = raw_cmd_ioctl(cmd, (void __user *)param);
-		if (i == -EINTR)
-			return -EINTR;
-		process_fd_request();
-		return i;
+		return floppy_raw_cmd_ioctl(type, drive, cmd, (void __user *)param);
 	case FDTWADDLE:
 		if (lock_fdc(drive))
 			return -EINTR;

programming_language: C