[BUG] Pointless String Length in prvCreateDNSMessage() Leads to Compiler Warning/Error

[StefanBalt]

Describe the bug

GCC (with strict settings) raises the following error

error: 'strncpy' specified bound depends on the length of the source argument [-Werror=stringop-overflow=]

for the line below

FreeRTOS-Plus-TCP/source/FreeRTOS_DNS.c

Line 1507 in fbb668a

( void ) strncpy( ( char * ) &( pucUDPPayloadBuffer[ uxIndex ] ), pcHostName, strlen( pcHostName ) + 1U );

and it is not wrong. Why use strncpy() if we do not have a useful length parameter in this scope?

I see 3 possible fixes:

1. Keep track of the destination buffer size after it is allocated in prvGetPayloadBuffer()
2. Use strcpy() again (revert change from 4c4223a)
3. Use memcpy()

[tony-josi-aws]

@StefanBalt, thanks for reporting this issue.

This change was done along with other strcpy replacements since its known that pucUDPPayloadBuffer is big enough to hold the pcHostName as its allocated with the size of pcHostName accounted for in the size calculation here.

Since its causing compiler warnings with strict settings, it makes sense to update it, probably back to strcpy or memcpy.

GCC version: gcc (Ubuntu 9.4.0-1ubuntu1~20.04.2) 9.4.0 doesn't produce this warning with any of the -Wstringop-overflow= types [0 to 4]. Are you using any other compiler flags?

[StefanBalt]

Any GCC >= 9.2 I tried raised a warning with -Wall -O2 flags. Lower optimization levels do not seem to warn interestingly.

Example in godbolt: https://godbolt.org/z/qaGdMGMKe

[ig15]

The issue has been fixed by the PR. Thanks @StefanBalt for bringing it up. Closing the issue.