scsi_put_cdrom_generic_arg() is copying uninitialized stack memory to
userspace, since the compiler may leave a 3-byte hole in the middle of
`cgc32`. Fix it by adding a padding field to `struct
compat_cdrom_generic_command`.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: f3ee6e63a9df ("compat_ioctl: move CDROM_SEND_PACKET handling into scsi")
Suggested-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Reported-by: syzbot+85433a479a646a064ab3@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Peilin Ye <yepeilin.cs@xxxxxxxxx>
---
v3: https://lore.kernel.org/lkml/20200909095057.1214104-1-yepeilin.cs@xxxxxxxxx/
Changes in v4:
- Change "Prevent" in the title to "Fix", and improve the commit
message, since syzbot has reported it as a "real" bug.
- Add syzbot Reported-by: tag.
Changes in v3:
- Improve commit message. scsi_put_cdrom_generic_arg() does not
*always* leak kernel information. It is compiler dependent.
Reference: https://www.nccgroup.com/us/about-us/newsroom-and-events/blog/2019/october/padding-the-struct-how-a-compiler-optimization-can-disclose-stack-memory/
- Base the patch against mainline 5.9-rc4.
Change in v2:
- Add a padding field to `struct compat_cdrom_generic_command`,
instead of doing memset() on `cgc32`. (Suggested by Jens Axboe
<axboe@xxxxxxxxx>)
$ # before
$ pahole -C "compat_cdrom_generic_command" !$
pahole -C "compat_cdrom_generic_command" block/scsi_ioctl.o
struct compat_cdrom_generic_command {
unsigned char cmd[12]; /* 0 12 */
compat_caddr_t buffer; /* 12 4 */
compat_uint_t buflen; /* 16 4 */
compat_int_t stat; /* 20 4 */
compat_caddr_t sense; /* 24 4 */
unsigned char data_direction; /* 28 1 */
/* XXX 3 bytes hole, try to pack */
compat_int_t quiet; /* 32 4 */
compat_int_t timeout; /* 36 4 */
compat_caddr_t reserved[1]; /* 40 4 */
/* size: 44, cachelines: 1, members: 9 */
/* sum members: 41, holes: 1, sum holes: 3 */
/* last cacheline: 44 bytes */
};
$ # after
$ pahole -C "compat_cdrom_generic_command" block/scsi_ioctl.o
struct compat_cdrom_generic_command {
unsigned char cmd[12]; /* 0 12 */
compat_caddr_t buffer; /* 12 4 */
compat_uint_t buflen; /* 16 4 */
compat_int_t stat; /* 20 4 */
compat_caddr_t sense; /* 24 4 */
unsigned char data_direction; /* 28 1 */
unsigned char pad[3]; /* 29 3 */
compat_int_t quiet; /* 32 4 */
compat_int_t timeout; /* 36 4 */
compat_caddr_t reserved[1]; /* 40 4 */
/* size: 44, cachelines: 1, members: 10 */
/* last cacheline: 44 bytes */
};
$ _
block/scsi_ioctl.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index ef722f04f88a..72108404718f 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -651,6 +651,7 @@ struct compat_cdrom_generic_command {
compat_int_t stat;
compat_caddr_t sense;
unsigned char data_direction;
+ unsigned char pad[3];
compat_int_t quiet;
compat_int_t timeout;
compat_caddr_t reserved[1];
--
2.25.1
