4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
commit 78aafb3884f6bc6636efcc1760c891c8500b9922 upstream.
There is a dead-lock in the hwrng device read path. This triggers
when the user reads from /dev/hwrng into memory also mmap-ed from
/dev/hwrng. The resulting page fault triggers a recursive read
which then dead-locks.
Fix this by using a stack buffer when calling copy_to_user.
Reported-by: Edward Adam Davis <eadavis@xxxxxx>
Reported-by: syzbot+c52ab18308964d248092@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 9996508b3353 ("hwrng: core - Replace u32 in driver API with byte array")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/hw_random/core.c | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -24,10 +24,13 @@
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/slab.h>
+#include <linux/string.h>
#include <linux/uaccess.h>
#define RNG_MODULE_NAME "hw_random"
+#define RNG_BUFFER_SIZE (SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES)
+
static struct hwrng *current_rng;
/* the current rng has been explicitly chosen by user via sysfs */
static int cur_rng_set_by_user;
@@ -59,7 +62,7 @@ static inline int rng_get_data(struct hw
static size_t rng_buffer_size(void)
{
- return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
+ return RNG_BUFFER_SIZE;
}
static void add_early_randomness(struct hwrng *rng)
@@ -202,6 +205,7 @@ static inline int rng_get_data(struct hw
static ssize_t rng_dev_read(struct file *filp, char __user *buf,
size_t size, loff_t *offp)
{
+ u8 buffer[RNG_BUFFER_SIZE];
ssize_t ret = 0;
int err = 0;
int bytes_read, len;
@@ -229,34 +233,37 @@ static ssize_t rng_dev_read(struct file
if (bytes_read < 0) {
err = bytes_read;
goto out_unlock_reading;
+ } else if (bytes_read == 0 &&
+ (filp->f_flags & O_NONBLOCK)) {
+ err = -EAGAIN;
+ goto out_unlock_reading;
}
+
data_avail = bytes_read;
}
- if (!data_avail) {
- if (filp->f_flags & O_NONBLOCK) {
- err = -EAGAIN;
- goto out_unlock_reading;
- }
- } else {
- len = data_avail;
+ len = data_avail;
+ if (len) {
if (len > size)
len = size;
data_avail -= len;
- if (copy_to_user(buf + ret, rng_buffer + data_avail,
- len)) {
+ memcpy(buffer, rng_buffer + data_avail, len);
+ }
+ mutex_unlock(&reading_mutex);
+ put_rng(rng);
+
+ if (len) {
+ if (copy_to_user(buf + ret, buffer, len)) {
err = -EFAULT;
- goto out_unlock_reading;
+ goto out;
}
size -= len;
ret += len;
}
- mutex_unlock(&reading_mutex);
- put_rng(rng);
if (need_resched())
schedule_timeout_interruptible(1);
@@ -267,6 +274,7 @@ static ssize_t rng_dev_read(struct file
}
}
out:
+ memzero_explicit(buffer, sizeof(buffer));
return ret ? : err;
out_unlock_reading:
