strparser: Fix signed/unsigned mismatch bug

The `len` member of the sk_buff is an unsigned int. This is cast to
`ssize_t` (a signed type) for the first sk_buff in the comparison,
but not the second sk_buff. On 32-bit systems, this can result in
an integer underflow for certain values because unsigned arithmetic
is being used.

This appears to be an oversight: if the intention was to use unsigned
arithmetic, then the first cast would have been omitted. The change
ensures both len values are cast to `ssize_t`.

The underflow causes an issue with ktls when multiple TLS PDUs are
included in a single TCP segment. The mainline kernel does not use
strparser for ktls anymore, but this is still useful for other
features that still use strparser, and for backporting.

Signed-off-by: Nate Karstens <nate.karstens@garmin.com>
Cc: stable@vger.kernel.org
Fixes: 43a0c6751a32 ("strparser: Stream parser for messages")
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20251106222835.1871628-1-nate.karstens@garmin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c
index 43b1f558b33dbd02130a8ed975e7805f519430cf..e659fea2da70f849352679d8575a6225c5733462 100644 (file)
--- a/net/strparser/strparser.c
+++ b/net/strparser/strparser.c
@@ -238,7 +238,7 @@ static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
                                strp_parser_err(strp, -EMSGSIZE, desc);
                                break;
                        } else if (len <= (ssize_t)head->len -
-                                         skb->len - stm->strp.offset) {
+                                         (ssize_t)skb->len - stm->strp.offset) {
                                /* Length must be into new skb (and also
                                 * greater than zero)
                                 */