[Linux-kernel-mentees] [PATCH] block/scsi-ioctl: Prevent kernel-infoleak in scsi_put_cdrom_generic_arg()

[Linux-kernel-mentees] [PATCH] block/scsi-ioctl: Prevent kernel-infoleak in scsi_put_cdrom_generic_arg()

[Peilin Ye]

scsi_put_cdrom_generic_arg() is copying uninitialized stack memory to
userspace due to the compiler not initializing holes in statically
allocated structures. Fix it by initializing `cgc32` using memset().

Cc: stable@vger.kernel.org
Fixes: f3ee6e63a9df ("compat_ioctl: move CDROM_SEND_PACKET handling into scsi")
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
---
 block/scsi_ioctl.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index ef722f04f88a..1b7f85634751 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -692,16 +692,19 @@ static int scsi_put_cdrom_generic_arg(const struct cdrom_generic_command *cgc,
 {
 #ifdef CONFIG_COMPAT
 	if (in_compat_syscall()) {
-		struct compat_cdrom_generic_command cgc32 = {
-			.buffer		= (uintptr_t)(cgc->buffer),
-			.buflen		= cgc->buflen,
-			.stat		= cgc->stat,
-			.sense		= (uintptr_t)(cgc->sense),
-			.data_direction	= cgc->data_direction,
-			.quiet		= cgc->quiet,
-			.timeout	= cgc->timeout,
-			.reserved[0]	= (uintptr_t)(cgc->reserved[0]),
-		};
+		struct compat_cdrom_generic_command cgc32;
+
+		memset(&cgc32, 0, sizeof(cgc32));
+
+		cgc32.buffer	= (uintptr_t)(cgc->buffer);
+		cgc32.buflen	= cgc->buflen;
+		cgc32.stat	= cgc->stat;
+		cgc32.sense	= (uintptr_t)(cgc->sense);
+		cgc32.data_direction	= cgc->data_direction;
+		cgc32.quiet	= cgc->quiet;
+		cgc32.timeout	= cgc->timeout;
+		cgc32.reserved[0]	= (uintptr_t)(cgc->reserved[0]);
+
 		memcpy(&cgc32.cmd, &cgc->cmd, CDROM_PACKET_SIZE);
 
 		if (copy_to_user(arg, &cgc32, sizeof(cgc32)))
-- 
2.25.1

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Re: [Linux-kernel-mentees] [PATCH] block/scsi-ioctl: Prevent kernel-infoleak in scsi_put_cdrom_generic_arg()

[Jens Axboe]

On 7/27/20 10:19 AM, Peilin Ye wrote:
> scsi_put_cdrom_generic_arg() is copying uninitialized stack memory to
> userspace due to the compiler not initializing holes in statically
> allocated structures. Fix it by initializing `cgc32` using memset().

Could also just add the appropriate pad, so the compiler does the
right thing.


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];

-- 
Jens Axboe

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[Linux-kernel-mentees] [PATCH v2] block/scsi-ioctl: Prevent kernel-infoleak in scsi_put_cdrom_generic_arg()

[Peilin Ye]

scsi_put_cdrom_generic_arg() is copying uninitialized stack memory to
userspace due to the compiler not initializing holes in statically
allocated structures. Fix it by adding a padding field to `struct
compat_cdrom_generic_command`.

Cc: stable@vger.kernel.org
Fixes: f3ee6e63a9df ("compat_ioctl: move CDROM_SEND_PACKET handling into scsi")
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
---
Change in v2:
    - Add a padding field to `struct compat_cdrom_generic_command`,
      instead of doing memset() on `cgc32`. (Suggested by Jens Axboe
      <axboe@kernel.dk>)

 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

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[Linux-kernel-mentees] [PATCH v3] block/scsi-ioctl: Prevent kernel-infoleak in scsi_put_cdrom_generic_arg()

[Peilin Ye]

scsi_put_cdrom_generic_arg() is potentially copying uninitialized stack
memory to userspace, since the compiler may leave a 3-byte hole in the
middle of `cgc32`. Prevent it by adding a padding field to `struct
compat_cdrom_generic_command`.

Cc: stable@vger.kernel.org
Fixes: f3ee6e63a9df ("compat_ioctl: move CDROM_SEND_PACKET handling into scsi")
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
---
Change 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@kernel.dk>)

$ # 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

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