[PATCH] Bluetooth: eir: validate service data length before reading UUID

[Aamir Ahmed]

eir_get_service_data() reads a 16-bit UUID from the service data using
get_unaligned_le16() without first checking that the data is long enough
to hold a UUID16 (2 bytes). If a malformed EIR entry has a service data
field with only 1 byte of payload (field_len=2), eir_get_data() returns
dlen=1. The subsequent get_unaligned_le16() then reads 1 byte past the
field boundary.

Additionally, if the corrupted UUID happens to match, the length
calculation "dlen - 2" underflows to SIZE_MAX since dlen is size_t.
Current callers either pass NULL for the length parameter or bounds-check
the returned length, but future callers may not.

Add a check that dlen >= sizeof(u16) and skip fields that are too short
to contain a valid UUID16.

Fixes: 8f9ae5b3ae80 ("Bluetooth: eir: Add helpers for managing service data")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Aamir Ahmed <elb12345@xxxxxxxxxxxxx>
---
 net/bluetooth/eir.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/eir.c b/net/bluetooth/eir.c
index a55696820b22..ee0136bfae40 100644
--- a/net/bluetooth/eir.c
+++ b/net/bluetooth/eir.c
@@ -373,7 +373,15 @@ void *eir_get_service_data(u8 *eir, size_t eir_len, u16 uuid, size_t *len)
 	size_t dlen;
 
 	while ((eir = eir_get_data(eir, eir_len, EIR_SERVICE_DATA, &dlen))) {
-		u16 value = get_unaligned_le16(eir);
+		u16 value;
+
+		if (dlen < sizeof(value)) {
+			eir += dlen;
+			eir_len = eir_end - eir;
+			continue;
+		}
+
+		value = get_unaligned_le16(eir);
 
 		if (uuid == value) {
 			if (len)
-- 
2.43.0