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Message-ID: <ZWqCAsCUGN1cFIIT@gondor.apana.org.au>
Date: Sat, 2 Dec 2023 09:01:54 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Edward Adam Davis <eadavis@...com>
Cc: davem@...emloft.net, linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org, olivia@...enic.com,
syzbot+c52ab18308964d248092@...kaller.appspotmail.com,
syzkaller-bugs@...glegroups.com,
Ian Molton <ian.molton@...labora.co.uk>,
Rusty Russell <rusty@...tcorp.com.au>
Subject: [PATCH] hwrng: core - Fix page fault dead lock on mmap-ed hwrng
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@...com>
Reported-by: syzbot+c52ab18308964d248092@...kaller.appspotmail.com
Fixes: 9996508b3353 ("hwrng: core - Replace u32 in driver API with byte array")
Cc: <stable@...r.kernel.org>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 420f155d251f..a3bbdd6e60fc 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -23,10 +23,13 @@
#include <linux/sched.h>
#include <linux/sched/signal.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;
@@ -58,7 +61,7 @@ static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
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)
@@ -209,6 +212,7 @@ static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
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;
@@ -236,34 +240,37 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
if (bytes_read < 0) {
err = bytes_read;
goto out_unlock_reading;
- }
- data_avail = bytes_read;
- }
-
- if (!data_avail) {
- if (filp->f_flags & O_NONBLOCK) {
+ } else if (bytes_read == 0 &&
+ (filp->f_flags & O_NONBLOCK)) {
err = -EAGAIN;
goto out_unlock_reading;
}
- } else {
- len = data_avail;
+
+ data_avail = bytes_read;
+ }
+
+ 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);
@@ -274,6 +281,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
}
}
out:
+ memzero_explicit(buffer, sizeof(buffer));
return ret ? : err;
out_unlock_reading:
--
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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