[NCLUG] newbie::Write to superblocks

[Yong Sun]

Hey Guys,

I am a programmer in Unix environment, but a newbie on Linux. We just
upgraded our redhat linux from 6.2 to 7.1, so I can access the over 2Gb
files. One run on the system made the superblock damaged. I am not sure
it is from my program, but my sys adm said I am the most likely
candidate. The program is simple like,

int fd = open(afile, O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0644);
int n1, n2, n3;
....
off64_t offset = (off64_t) (n1*n2*n3*sizeof(float)); // here
n1*n2*n3*sizeof(float) could overflow
if(lseek64(fd, offset, SEEK_SET) != offset) exit(-1);
write(fd, blablah...);

The argument is that the offset could be a big negative number, so it
seeked to it and it is in superblock...

Is that true? If yes, the file system will have no protection at all!

Thanks,
Yong