[PATCH v2 1/6] bitmap: bitmap_parse(): reject non-hex character before 8 digits

[Shashank Mohan Jain]

bitmap_parse() is documented to return -EINVAL for illegal characters,
and it does so everywhere except when the illegal character directly
precedes a chunk of exactly eight hex digits.

bitmap_get_x32_reverse() parses a chunk from right to left.  After it
has consumed eight digits it looks at one more character: a hex digit
means the chunk is wider than 32 bits and -EOVERFLOW is returned.  Any
other character is silently consumed as if it were a separator, and the
remaining input is parsed as the next chunk.  As a result:

  "x12345678"   -> 0x12345678, returns 0 (expected -EINVAL)
  "1g12345678"  -> 0x1_12345678, returns 0 (expected -EINVAL)
  "0x0000000f"  -> 0xf, returns 0, while "0xf" returns -EINVAL

bitmap_parse() backs cpumask_parse() and cpumask_parse_user(), so the
same inconsistency is visible when writing masks such as
/proc/irq/*/smp_affinity or the network queue rps_cpus/xps_cpus files.

__bitmap_parse(), which this function replaced in commit 2d6261583be0
("lib: rework bitmap_parse()"), rejected all three strings with -EINVAL,
and a "0x" prefix is accepted today only when exactly eight digits
follow it, so no reliably working input is lost.

When the loop falls through, *end is known to be a non-separator
character inside the buffer, so return -EOVERFLOW if it is a hex digit
and -EINVAL otherwise.

Fixes: 2d6261583be0 ("lib: rework bitmap_parse()")
Assisted-by: LLM
Signed-off-by: Shashank Mohan Jain <jain.sm@xxxxxxxxx>
---
 lib/bitmap-str.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/bitmap-str.c b/lib/bitmap-str.c
index dd9aa0635fa5..e02c5bc80951 100644
--- a/lib/bitmap-str.c
+++ b/lib/bitmap-str.c
@@ -414,8 +414,12 @@ static const char *bitmap_get_x32_reverse(const char *start,
 			goto out;
 	}
 
-	if (hex_to_bin(*end--) >= 0)
-		return ERR_PTR(-EOVERFLOW);
+	/*
+	 * Eight digits have been consumed and the next character is not a
+	 * separator: another hex digit means the chunk does not fit in 32
+	 * bits, anything else is an illegal character.
+	 */
+	return ERR_PTR(hex_to_bin(*end) >= 0 ? -EOVERFLOW : -EINVAL);
 out:
 	*num = ret;
 	return end;
-- 
2.43.0