linux-kernel - [PATCH 3/6] device-mapper: structs and parameter strings must not overlap

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Message-Id: <20230601212456.1533-4-demi@invisiblethingslab.com>
Date:   Thu,  1 Jun 2023 17:24:52 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com
Cc:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH 3/6] device-mapper: structs and parameter strings must not overlap

The NUL terminator for each target parameter string must precede the
following 'struct dm_target_spec'.  Otherwise, dm_split_args() might
corrupt this struct.  Furthermore, the first 'struct dm_target_spec'
must come after the 'struct dm_ioctl', as if it overlaps too much
dm_split_args() could corrupt the 'struct dm_ioctl'.

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 | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 64e8f16d344c47057de5e2d29e3d63202197dca0..da6ca26b51d0953df380582bb3a51c2ec22c27cb 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
@@ -1423,10 +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);
 
-	if (*spec < (last + 1))
-		return -EINVAL;
-
-	return invalid_str(*target_params, end);
+	return 0;
 }
 
 static int populate_table(struct dm_table *table,
@@ -1436,8 +1433,9 @@ 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__);
@@ -1445,6 +1443,13 @@ static int populate_table(struct dm_table *table,
 	}
 
 	for (i = 0; i < param->target_count; i++) {
+		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;
+		}
 
 		r = next_target(spec, next, end, &spec, &target_params);
 		if (r) {
@@ -1452,6 +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 = (size_t)(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