linux-kernel - [PATCH v2] pcd: do not leak information in ioctl

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Date:   Mon, 11 Apr 2022 13:50:26 -0400
From:   Tom Rix <trix@...hat.com>
To:     tim@...erelk.net, axboe@...nel.dk, nathan@...nel.org,
        ndesaulniers@...gle.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Tom Rix <trix@...hat.com>
Subject: [PATCH v2] pcd: do not leak information in ioctl

clang static analysis reports this representative issue
pcd.c:832:22: warning: Assigned value is garbage
  or undefined
  tochdr->cdth_trk0 = buffer[2];
                    ^ ~~~~~~~~~

If the call to pcd_atapi fails, buffer is an unknown
state.  Passing an unknown buffer back to the user
can leak information and is a security risk.

Check before returning this buffer to the user.

The per-case variables cmd and buffer are common.
Change their scope to function level.
Change colliding parameter name cmd to request.

Cleanup whitespace
Additionally initialize the buffer to zero.

This problem can be seen in the 2.4.0 kernel
However this scm only goes back as far as 2.6.12

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Tom Rix <trix@...hat.com>
---
v2: split from combined scsi,pcd patch

 drivers/block/paride/pcd.c | 87 +++++++++++++++++---------------------
 1 file changed, 38 insertions(+), 49 deletions(-)

diff --git a/drivers/block/paride/pcd.c b/drivers/block/paride/pcd.c
index f462ad67931a..2315918e3647 100644
--- a/drivers/block/paride/pcd.c
+++ b/drivers/block/paride/pcd.c
@@ -810,67 +810,56 @@ static void do_pcd_read_drq(void)
 
 /* the audio_ioctl stuff is adapted from sr_ioctl.c */
 
-static int pcd_audio_ioctl(struct cdrom_device_info *cdi, unsigned int cmd, void *arg)
+static int pcd_audio_ioctl(struct cdrom_device_info *cdi, unsigned int request, void *arg)
 {
 	struct pcd_unit *cd = cdi->handle;
+	char cmd[12] = { GPCMD_READ_TOC_PMA_ATIP, 0, 0, 0, 0, 0, 0, 0, 12, 0, 0, 0 };
+	char buffer[32] = {};
 
-	switch (cmd) {
-
+	switch (request) {
 	case CDROMREADTOCHDR:
+	{
+		struct cdrom_tochdr *tochdr =
+			(struct cdrom_tochdr *) arg;
 
-		{
-			char cmd[12] =
-			    { GPCMD_READ_TOC_PMA_ATIP, 0, 0, 0, 0, 0, 0, 0, 12,
-			 0, 0, 0 };
-			struct cdrom_tochdr *tochdr =
-			    (struct cdrom_tochdr *) arg;
-			char buffer[32];
-			int r;
-
-			r = pcd_atapi(cd, cmd, 12, buffer, "read toc header");
+		if (pcd_atapi(cd, cmd, 12, buffer, "read toc header"))
+			return -EIO;
 
-			tochdr->cdth_trk0 = buffer[2];
-			tochdr->cdth_trk1 = buffer[3];
+		tochdr->cdth_trk0 = buffer[2];
+		tochdr->cdth_trk1 = buffer[3];
 
-			return r ? -EIO : 0;
-		}
+		return 0;
+	}
 
 	case CDROMREADTOCENTRY:
-
-		{
-			char cmd[12] =
-			    { GPCMD_READ_TOC_PMA_ATIP, 0, 0, 0, 0, 0, 0, 0, 12,
-			 0, 0, 0 };
-
-			struct cdrom_tocentry *tocentry =
-			    (struct cdrom_tocentry *) arg;
-			unsigned char buffer[32];
-			int r;
-
-			cmd[1] =
-			    (tocentry->cdte_format == CDROM_MSF ? 0x02 : 0);
-			cmd[6] = tocentry->cdte_track;
-
-			r = pcd_atapi(cd, cmd, 12, buffer, "read toc entry");
-
-			tocentry->cdte_ctrl = buffer[5] & 0xf;
-			tocentry->cdte_adr = buffer[5] >> 4;
-			tocentry->cdte_datamode =
-			    (tocentry->cdte_ctrl & 0x04) ? 1 : 0;
-			if (tocentry->cdte_format == CDROM_MSF) {
-				tocentry->cdte_addr.msf.minute = buffer[9];
-				tocentry->cdte_addr.msf.second = buffer[10];
-				tocentry->cdte_addr.msf.frame = buffer[11];
-			} else
-				tocentry->cdte_addr.lba =
-				    (((((buffer[8] << 8) + buffer[9]) << 8)
-				      + buffer[10]) << 8) + buffer[11];
-
-			return r ? -EIO : 0;
+	{
+		struct cdrom_tocentry *tocentry =
+			(struct cdrom_tocentry *) arg;
+
+		cmd[1] = (tocentry->cdte_format == CDROM_MSF ? 0x02 : 0);
+		cmd[6] = tocentry->cdte_track;
+
+		if (pcd_atapi(cd, cmd, 12, buffer, "read toc entry"))
+			return -EIO;
+
+		tocentry->cdte_ctrl = buffer[5] & 0xf;
+		tocentry->cdte_adr = buffer[5] >> 4;
+		tocentry->cdte_datamode =
+			(tocentry->cdte_ctrl & 0x04) ? 1 : 0;
+		if (tocentry->cdte_format == CDROM_MSF) {
+			tocentry->cdte_addr.msf.minute = buffer[9];
+			tocentry->cdte_addr.msf.second = buffer[10];
+			tocentry->cdte_addr.msf.frame = buffer[11];
+		} else {
+			tocentry->cdte_addr.lba =
+				(((((buffer[8] << 8) + buffer[9]) << 8)
+				  + buffer[10]) << 8) + buffer[11];
 		}
 
-	default:
+		return 0;
+	}
 
+	default:
 		return -ENOSYS;
 	}
 }
-- 
2.27.0