From: "Jason A. Donenfeld" Jason@zx2c4.com
stable inclusion from stable-v5.10.119 commit 514f587340010942e7d22f2a51b8c812399e4ce7 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6BB
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit 1ce6c8d68f8ac587f54d0a271ac594d3d51f3efb upstream.
get_random_bytes_user() checks for signals after producing a PAGE_SIZE worth of output, just like /dev/zero does. write_pool() is doing basically the same work (actually, slightly more expensive), and so should stop to check for signals in the same way. Let's also name it write_pool_user() to match get_random_bytes_user(), so this won't be misused in the future.
Before this patch, massive writes to /dev/urandom would tie up the process for an extremely long time and make it unterminatable. After, it can be successfully interrupted. The following test program can be used to see this works as intended:
#include <unistd.h> #include <fcntl.h> #include <signal.h> #include <stdio.h>
static unsigned char x[~0U];
static void handle(int) { }
int main(int argc, char *argv[]) { pid_t pid = getpid(), child; int fd; signal(SIGUSR1, handle); if (!(child = fork())) { for (;;) kill(pid, SIGUSR1); } fd = open("/dev/urandom", O_WRONLY); pause(); printf("interrupted after writing %zd bytes\n", write(fd, x, sizeof(x))); close(fd); kill(child, SIGTERM); return 0; }
Result before: "interrupted after writing 2147479552 bytes" Result after: "interrupted after writing 4096 bytes"
Cc: Dominik Brodowski linux@dominikbrodowski.net Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com Acked-by: Xie XiuQi xiexiuqi@huawei.com --- drivers/char/random.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c index b3ce4201a51f..00b50ccc9fae 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1255,7 +1255,7 @@ static __poll_t random_poll(struct file *file, poll_table *wait) return crng_ready() ? EPOLLIN | EPOLLRDNORM : EPOLLOUT | EPOLLWRNORM; }
-static ssize_t write_pool(struct iov_iter *iter) +static ssize_t write_pool_user(struct iov_iter *iter) { u8 block[BLAKE2S_BLOCK_SIZE]; ssize_t ret = 0; @@ -1270,7 +1270,13 @@ static ssize_t write_pool(struct iov_iter *iter) mix_pool_bytes(block, copied); if (!iov_iter_count(iter) || copied != sizeof(block)) break; - cond_resched(); + + BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0); + if (ret % PAGE_SIZE == 0) { + if (signal_pending(current)) + break; + cond_resched(); + } }
memzero_explicit(block, sizeof(block)); @@ -1279,7 +1285,7 @@ static ssize_t write_pool(struct iov_iter *iter)
static ssize_t random_write_iter(struct kiocb *kiocb, struct iov_iter *iter) { - return write_pool(iter); + return write_pool_user(iter); }
static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter) @@ -1346,7 +1352,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) ret = import_single_range(WRITE, p, len, &iov, &iter); if (unlikely(ret)) return ret; - ret = write_pool(&iter); + ret = write_pool_user(&iter); if (unlikely(ret < 0)) return ret; /* Since we're crediting, enforce that it was all written into the pool. */