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gateway/uplink: bound writes against the block-pool constant #313

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gateway/uplink: bound writes against the block-pool constant #313

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8 changes: 8 additions & 0 deletions src/block.h
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,14 @@
/** Maximum ciphertext size without the length of the size field */
#define MAX_BLOCK_SIZE_FIELD_VALUE (MAX_CIPHERTEXT_BLOCK_SIZE - sizeof(uint16_t))

/*
* CONFIG_POUCH_BLOCK_SIZE feeds LOG2() above, which rounds DOWN to a power of two.
* A non-power-of-two value silently yields a smaller block everywhere it is used. Reject it at build
* time so the configured size is the size actually used.
*/
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POUCH_STATIC_ASSERT((CONFIG_POUCH_BLOCK_SIZE & (CONFIG_POUCH_BLOCK_SIZE - 1)) == 0,
"CONFIG_POUCH_BLOCK_SIZE must be a power of two");

@trond-snekvik trond-snekvik Sep 2, 2026

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I actually explicitly want to avoid this, as the rounding down is deliberate on the device side. As the block size always has to be a power of two, rounding down works well here as well, as long as we account for it when calculating the capacity of the block.

I made a counter proposal for this problem in #336, which changes the uplink module to use the appropriate block API for calculating the capacity of the buffer.


int block_decode_hdr(struct pouch_bufview *v,
uint16_t *block_size,
uint8_t *stream_id,
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7 changes: 4 additions & 3 deletions src/gateway/uplink.c
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@

#include "uplink.h"
#include "../buf.h"
#include "../block.h"

POUCH_LOG_REGISTER(gw_uplink, CONFIG_POUCH_GATEWAY_LOG_LEVEL);

Expand Down Expand Up @@ -191,11 +192,11 @@ static void send_uplink_via_cloud(struct pouch_gateway_uplink *uplink)
}

/*
* Max bytes per gateway block. Each pouch_buf slot holds at least
* CONFIG_POUCH_BLOCK_SIZE bytes; we conservatively use that as the
* Max payload bytes per gateway block. Each pouch_buf slot holds at least
* MAX_BLOCK_PAYLOAD_SIZE bytes; we conservatively use that as the
* per-block capacity.
*/
#define GW_BLOCK_MAX_BYTES CONFIG_POUCH_BLOCK_SIZE
#define GW_BLOCK_MAX_BYTES MAX_BLOCK_PAYLOAD_SIZE

int pouch_gateway_uplink_write(struct pouch_gateway_uplink *uplink,
const uint8_t *payload,
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