MMAP reading and writing files - c

Question

Im trying to use mmap to read in a file and then encrypt it and then write the encryption to the output file. I'm trying to also do this with mmap but when I run the code, it tells me that it was not able to unmmap due to "Invalid Argument".
//Open files initialy and obtain a handle to the file.
inputFile = open(inFileName, O_RDONLY, S_IREAD);
outputFile = open(outFileName, O_APPEND | O_CREAT | O_TRUNC | O_WRONLY, S_IWRITE);
//Allocate buffers for encrption.
from = (unsigned char*)malloc(blockSize);
to = (unsigned char*)malloc(blockSize);
mmapWriteBuff = (unsigned char*)malloc(blockSize);
mmapReadBuff = (unsigned char*)malloc(blockSize);
memset(to, 0, blockSize);
memset(from, 0, blockSize);
memset(mmapWriteBuff, 0, blockSize);
memset(mmapReadBuff, 0, blockSize);
//Make sure we have permission to read the file provided.
setFilePermissions(inFileName, PERMISSION_MODE);
setFilePermissions(outFileName, PERMISSION_MODE);
if(encriptParam)
{
printf("*Encripting file: %s *\n", inFileName);
do//Go through the entire file.
{
if(memParam)
{
currAmt = lseek(inputFile, blockSize, SEEK_SET);
mmapReadBuff = mmap(0, blockSize, PROT_READ, MAP_SHARED, inputFile, 0);
/*
*This is how you encrypt an input char* buffer "from", of length "len"
*onto output buffer "to", using key "key". Jyst pass "iv" and "&n" as
*shown, and don't forget to actually tell the function to BF_ENCRYPT.
*/
BF_cfb64_encrypt(mmapReadBuff, mmapWriteBuff, blockSize, &key, iv, &n, BF_ENCRYPT);
if(currAmt < blockSize)
{
writeAmt = lseek(outputFile, currAmt, SEEK_SET);
mmapWriteBuff = mmap(0, currAmt, PROT_WRITE, MAP_SHARED, outputFile, 0);
if(errno == EINVAL)
{
perror("MMAP failed to start write buffer: ");
exit(MMAP_IO_ERROR);
}
}
else
{
writeAmt = lseek(outputFile, blockSize, SEEK_SET);
mmapWriteBuff = mmap(0, blockSize, PROT_WRITE, MAP_SHARED, outputFile, 0);
if(errno == EINVAL)
{
perror("MMAP failed to start write buffer: ");
exit(MMAP_IO_ERROR);
}
}
mmapWriteBuff = to;
}
else
{
currAmt = read(inputFile, from, blockSize);
/*
*This is how you encrypt an input char* buffer "from", of length "len" *onto output buffer "to", using key "key". Jyst pass "iv" and "n" as
*shown, and don't forget to actually tell the function to BF_ENCRYT.
*/
BF_cfb64_encrypt(from, to, blockSize, &key, iv, &n, BF_ENCRYPT);
if(currAmt < blockSize)
{
writeAmt = write(outputFile, to, currAmt);
}
else
{
writeAmt = write(outputFile, to, blockSize);
}
}
if(memParam)
{
//if(currAmt < blockSize)
//{
// if(munmap(mmapWriteBuff, currAmt) == -1)
// {
// perror("MMAP failed to unmap itself: ");
//
// exit(MMAP_IO_ERROR);
// }
//
// if(munmap(mmapReadBuff, currAmt) == -1)
// {
// perror("MMAP failed to unmap itself: ");
//
// exit(MMAP_IO_ERROR);
// }
//}
//else
//{
if(munmap(mmapReadBuff, blockSize) == -1)
{
perror("MMAP Read Buffer failed to unmap itself: ");
exit(MMAP_IO_ERROR);
}
if(munmap(mmapWriteBuff, blockSize) == -1)
{
perror("MMAP Write Buffer failed to unmap itself: ");
exit(MMAP_IO_ERROR);
}
//}
}
memset(to, 0, strlen((char *)to));
memset(from, 0, strlen((char *)from));
memset(mmapReadBuff, 0, strlen((char*)mmapReadBuff));
memset(mmapWriteBuff, 0, strlen((char*)mmapWriteBuff));
}
while(currAmt > 0);
printf("*Saving file: %s *\n", outFileName);
}

Answer 1

Generally speaking, it seems like you might want to try setting up the outputFile file descriptor without the O_WRONLY flag. Using the O_WRONLY flag for mmap() isn't sufficient.
Thus, you may need to change this:
outputFile = open(outFileName, O_APPEND | O_CREAT | O_TRUNC | O_WRONLY, S_IWRITE);
to this:
outputFile = open(outFileName, O_APPEND | O_CREAT | O_TRUNC | O_RDWR, S_IWRITE);
I am not an expert with mmap(), but I know that you might want to give it both read and write permissions when opening the file descriptor.
EDIT:
Also you want want to try casting every mmap() call to (int*) like so:
mmapReadBuff = (int*)mmap(0, blockSize, PROT_READ, MAP_SHARED, inputFile, 0);