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isobusfs: srv: pad short Read File responses within the allocated buffer

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The Read File response buffer was allocated for the response header and
the requested data only. Short responses (e.g. count = 0) are extended to
ISOBUSFS_MIN_TRANSFER_LENGH which read beyond the allocated buffer and
sent heap content to the client.

Allocate at least ISOBUSFS_MIN_TRANSFER_LENGH bytes and fill the unused
bytes with 0xff.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
This commit is contained in:
Oliver Hartkopp
2026-10-14 10:21:56 +00:00
parent 33f7ddb5ed
commit d5571a5bc3
1 changed files with 12 additions and 2 deletions
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isobusfs/isobusfs_srv_fa.c
+12 -2
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@@ -739,6 +739,7 @@ static int isobusfs_srv_fa_rf_req(struct isobusfs_srv_priv *priv,
uint8_t error_code = 0;
ssize_t send_size;
bool res_allocated = false;
size_t alloc_size;
size_t max_bytes = 0;
uint16_t count = 0;
int ret = 0;
@@ -783,7 +784,12 @@ static int isobusfs_srv_fa_rf_req(struct isobusfs_srv_priv *priv,
max_bytes = count;
}
res = malloc(sizeof(*res) + max_bytes);
/* the response is padded to ISOBUSFS_MIN_TRANSFER_LENGH (see below) */
alloc_size = sizeof(*res) + max_bytes;
if (alloc_size < ISOBUSFS_MIN_TRANSFER_LENGH)
alloc_size = ISOBUSFS_MIN_TRANSFER_LENGH;
res = malloc(alloc_size);
if (!res) {
pr_warn("failed to allocate memory");
res = (struct isobusfs_read_file_response *)&res_fail[0];
@@ -823,8 +829,12 @@ send_response:
res->count = htole16(readed_size);
send_size = sizeof(*res) + readed_size;
if (send_size < ISOBUSFS_MIN_TRANSFER_LENGH)
if (send_size < ISOBUSFS_MIN_TRANSFER_LENGH) {
/* fill the unused bytes with 0xff */
memset((uint8_t *)res + send_size, 0xff,
ISOBUSFS_MIN_TRANSFER_LENGH - send_size);
send_size = ISOBUSFS_MIN_TRANSFER_LENGH;
}
/* send to socket */
ret = isobusfs_srv_sendto(priv, msg, res, send_size);