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Mix in the current random seed when writing the new one. 

This behavior lets the sysadmin add entropy to the random seed effective
after the next reboot.
This commit is contained in:
Jonas 'Sortie' Termansen 2023-04-04 20:49:34 +02:00
parent cb88c18bf0
commit 755f2cf539
1 changed files with 6 additions and 2 deletions
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8
init/init.c
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@ -2549,7 +2549,7 @@ static void write_random_seed(void)
{
const char* will_not = "next boot will not have fresh randomness";
const char* path = "/boot/random.seed";
int fd = open(path, O_WRONLY | O_CREAT | O_NOFOLLOW, 0600);
int fd = open(path, O_RDWR | O_CREAT | O_NOFOLLOW, 0600);
if ( fd < 0 )
{
if ( errno != ENOENT && errno != EROFS )
@ -2568,6 +2568,10 @@ static void write_random_seed(void)
close(fd);
return;
}
// Mix in the old random seed so the sysadmin can add new randomness here.
unsigned char old[256] = {0};
readall(fd, old, sizeof(old));
lseek(fd, 0, SEEK_SET);
// Write out randomness, but mix in some fresh kernel randomness in case the
// randomness used to seed arc4random didn't have enough entropy, there may
// be more now.
@ -2576,7 +2580,7 @@ static void write_random_seed(void)
unsigned char newbuf[256];
getentropy(newbuf, sizeof(newbuf));
for ( size_t i = 0; i < 256; i++ )
buf[i] ^= newbuf[i];
buf[i] ^= newbuf[i] ^ old[i];
size_t done = writeall(fd, buf, sizeof(buf));
explicit_bzero(buf, sizeof(buf));
if ( done < sizeof(buf) )