[PATCH v2 3/6] bitmap: bitmap_parselist(): reject trailing characters after group size

[Shashank Mohan Jain]

bitmap_parse_region() checks that every region ends at a separator
(',', whitespace, '\n' or '\0'), except in the "range:used/group" form:
after parsing the group size it returns the pointer to the following
character without looking at it.  The caller then starts a new region
at that character.

Before 'N' and 'all' were accepted as region starts this happened to be
harmless, because any other character would fail to parse as a new
region.  Now text directly following the group size is silently parsed
as another region:

  "0-7:1/2N"    -> bits 0,2,4,6,7 (nbits = 8), returns 0
  "0-7:1/2all"  -> all bits set, returns 0

while "0-7N", "5N" or "0-7:1/2x" are correctly rejected with -EINVAL.
bitmap_parselist() is documented to return -EINVAL for an invalid
character.  It parses cpu lists from sysfs, cgroup cpuset files and
boot parameters such as isolcpus= and nohz_full=, so a typo there is
accepted and yields a different mask than intended.

Check for the end of the region after the group size as well, like the
other forms do.

Fixes: 2c4885d24e64 ("lib: bitmap: support "N" as an alias for size of bitmap")
Assisted-by: LLM
Signed-off-by: Shashank Mohan Jain <jain.sm@xxxxxxxxx>
---
 lib/bitmap-str.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/bitmap-str.c b/lib/bitmap-str.c
index e02c5bc80951..b58966864657 100644
--- a/lib/bitmap-str.c
+++ b/lib/bitmap-str.c
@@ -299,7 +299,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
 	if (*str != '/')
 		return ERR_PTR(-EINVAL);
 
-	return bitmap_getnum(str + 1, &r->group_len, lastbit);
+	str = bitmap_getnum(str + 1, &r->group_len, lastbit);
+	if (IS_ERR(str))
+		return str;
+
+	if (!end_of_region(*str))
+		return ERR_PTR(-EINVAL);
+
+	return end_of_str(*str) ? NULL : str;
 
 no_end:
 	r->end = r->start;
-- 
2.43.0