linux-kernel - [PATCH v2 05/16] device-mapper: Target parameters must not overlap next target spec

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Message-Id: <20230530203116.2008-6-demi@invisiblethingslab.com>
Date:   Tue, 30 May 2023 16:31:05 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Roger Pau Monné <roger.pau@...rix.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com
Cc:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        stable@...r.kernel.org
Subject: [PATCH v2 05/16] device-mapper: Target parameters must not overlap next target spec

The NUL terminator for each target parameter string must preceed the
following 'struct dm_target_spec'.  Otherwise, dm_split_args() might
corrupt this struct.

Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
---
 drivers/md/dm-ioctl.c | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 9f505abba3dc22bffc6acb335c0bf29fec288fd5..491ef55b9e8662c3b02a2162b8c93ee086c078a1 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1391,7 +1391,7 @@ static inline fmode_t get_mode(struct dm_ioctl *param)
 	return mode;
 }
 
-static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
+static int next_target(struct dm_target_spec *last, uint32_t next, const char *end,
 		       struct dm_target_spec **spec, char **target_params)
 {
 	static_assert(_Alignof(struct dm_target_spec) <= 8,
@@ -1404,7 +1404,7 @@ static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
 	 * sizeof(struct dm_target_spec) or more, as otherwise *last was
 	 * out of bounds already.
 	 */
-	size_t remaining = (char *)end - (char *)last;
+	size_t remaining = end - (char *)last;
 
 	/*
 	 * There must be room for both the next target spec and the
@@ -1423,7 +1423,7 @@ static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
 	*spec = (struct dm_target_spec *) ((unsigned char *) last + next);
 	*target_params = (char *) (*spec + 1);
 
-	return invalid_str(*target_params, end);
+	return 0;
 }
 
 static int populate_table(struct dm_table *table,
@@ -1433,24 +1433,21 @@ static int populate_table(struct dm_table *table,
 	unsigned int i = 0;
 	struct dm_target_spec *spec = (struct dm_target_spec *) param;
 	uint32_t next = param->data_start;
-	void *end = (void *) param + param_size;
+	const char *const end = (const char *) param + param_size;
 	char *target_params;
+	size_t min_size = sizeof(struct dm_ioctl);
 
 	if (!param->target_count) {
 		DMERR("%s: no targets specified", __func__);
 		return -EINVAL;
 	}
 
-	if (next < sizeof(struct dm_ioctl)) {
-		DMERR("%s: first target spec (offset %u) overlaps 'struct dm_ioctl'",
-		      __func__, next);
-		return -EINVAL;
-	}
-
 	for (i = 0; i < param->target_count; i++) {
-		if (next < sizeof(*spec)) {
-			DMERR("%s: next target spec (offset %u) overlaps 'struct dm_target_spec'",
-			      __func__, next);
+		const char *nul_terminator;
+
+		if (next < min_size) {
+			DMERR("%s: next target spec (offset %u) overlaps %s",
+			      __func__, next, i ? "previous target" : "'struct dm_ioctl'");
 			return -EINVAL;
 		}
 
@@ -1460,6 +1457,15 @@ static int populate_table(struct dm_table *table,
 			return r;
 		}
 
+		nul_terminator = memchr(target_params, 0, (size_t)(end - target_params));
+		if (nul_terminator == NULL) {
+			DMERR("%s: target parameters not NUL-terminated", __func__);
+			return -EINVAL;
+		}
+
+		/* Add 1 for NUL terminator */
+		min_size = (nul_terminator - (const char *)spec) + 1;
+
 		r = dm_table_add_target(table, spec->target_type,
 					(sector_t) spec->sector_start,
 					(sector_t) spec->length,
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab