Rather than having getrandom() be called in a loop that handles EINTR --
which would require more code bloat -- we just limit the maximum seed
size to 256 bytes, which the kernel guarantees won't be interrupted.
Additionally document the flock() usage so that somebody doesn't remove
it.
Cc: Denys Vlasenko <vda.li...@googlemail.com>
Cc: Bernhard Reutner-Fischer <rep.dot....@gmail.com>
Signed-off-by: Jason A. Donenfeld <ja...@zx2c4.com>
---
util-linux/seedrng.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/util-linux/seedrng.c b/util-linux/seedrng.c
index c42274759..1257cd941 100644
--- a/util-linux/seedrng.c
+++ b/util-linux/seedrng.c
@@ -56,7 +56,7 @@
enum {
MIN_SEED_LEN = SHA256_OUTSIZE,
- MAX_SEED_LEN = 512
+ MAX_SEED_LEN = 256 /* Maximum size of getrandom() call without EINTR. */
};
static size_t determine_optimal_seed_len(void)
@@ -190,6 +190,8 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[])
if (mkdir(seed_dir, 0700) < 0 && errno != EEXIST)
bb_perror_msg_and_die("can't %s seed directory", "create");
dfd = open(seed_dir, O_DIRECTORY | O_RDONLY);
+ /* The flock() here is absolutely necessary, as the consistency of this
+ * program breaks down with concurrent uses. */
if (dfd < 0 || flock(dfd, LOCK_EX) < 0)
bb_perror_msg_and_die("can't %s seed directory", "lock");
xfchdir(dfd);
--
2.35.1
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