dm: reject trailing characters in sccanf input

Device mapper uses sscanf to convert arguments to numbers. The problem is that
the way we use it ignores additional unmatched characters in the scanned string.

For example, this `if (sscanf(string, "%d", &number) == 1)' will match a number,
but also it will match number with some garbage appended, like "123abc".

As a result, device mapper accepts garbage after some numbers. For example
the command `dmsetup create vg1-new --table "0 16384 linear 254:1bla 34816bla"'
will pass without an error.

This patch fixes all sscanf uses in device mapper. It appends "%c" with
a pointer to a dummy character variable to every sscanf statement.

The construct `if (sscanf(string, "%d%c", &number, &dummy) == 1)' succeeds
only if string is a null-terminated number (optionally preceded by some
whitespace characters). If there is some character appended after the number,
sscanf matches "%c", writes the character to the dummy variable and returns 2.
We check the return value for 1 and consequently reject numbers with some
garbage appended.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/md/dm-service-time.c b/drivers/md/dm-service-time.c
index 59883bd78214..9df8f6bd6418 100644
--- a/drivers/md/dm-service-time.c
+++ b/drivers/md/dm-service-time.c
@@ -110,6 +110,7 @@ static int st_add_path(struct path_selector *ps, struct dm_path *path,
         struct path_info *pi;
         unsigned repeat_count = ST_MIN_IO;
         unsigned relative_throughput = 1;
+        char dummy;
 
         /*
          * Arguments: [<repeat_count> [<relative_throughput>]]
@@ -128,13 +129,13 @@ static int st_add_path(struct path_selector *ps, struct dm_path *path,
                 return -EINVAL;
         }
 
-        if (argc && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
+        if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
                 *error = "service-time ps: invalid repeat count";
                 return -EINVAL;
         }
 
         if ((argc == 2) &&
-            (sscanf(argv[1], "%u", &relative_throughput) != 1 ||
+            (sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 ||
              relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
                 *error = "service-time ps: invalid relative_throughput value";
                 return -EINVAL;