[PATCH BlueZ v1 1/4] gatt-server: Check prepare write length before reallocating

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

append_prep_data() grew the buffer and copied the new fragment into it
before rejecting a total length above UINT16_MAX. On overflow the
allocation had already been enlarged and written while prep_data->length
was left at its previous value, desynchronising the buffer from its
tracked size.

Move the bound check ahead of the realloc() so an oversized prepare
write queue is rejected without touching the buffer.

Assisted-by: opencode:claude-opus-5
---
 src/shared/gatt-server.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/shared/gatt-server.c b/src/shared/gatt-server.c
index 516fceb8ed00..fde791aae867 100644
--- a/src/shared/gatt-server.c
+++ b/src/shared/gatt-server.c
@@ -1207,6 +1207,8 @@ static bool append_prep_data(struct prep_write_data *prep_data, uint16_t handle,
 		return true;
 
 	len = (size_t)prep_data->length + (size_t)length;
+	if (len > UINT16_MAX)
+		return false;
 
 	val = realloc(prep_data->value, len);
 	if (!val)
@@ -1215,9 +1217,6 @@ static bool append_prep_data(struct prep_write_data *prep_data, uint16_t handle,
 	memcpy(val + prep_data->length, value, length);
 
 	prep_data->value = val;
-
-	if (len > UINT16_MAX)
-		return false;
 	prep_data->length = (uint16_t)len;
 
 	return true;
-- 
2.55.0