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authorHerbert Xu <herbert@gondor.apana.org.au>2023-12-02 04:01:54 +0300
committerHerbert Xu <herbert@gondor.apana.org.au>2023-12-08 06:59:45 +0300
commit78aafb3884f6bc6636efcc1760c891c8500b9922 (patch)
tree89919fa3bb6a915e2c1b3eb2031581adb02fd6a5 /drivers/char
parent01d70a4bbff20ea05cadb4c208841985a7cc6596 (diff)
downloadlinux-78aafb3884f6bc6636efcc1760c891c8500b9922.tar.xz
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@qq.com> Reported-by: syzbot+c52ab18308964d248092@syzkaller.appspotmail.com Fixes: 9996508b3353 ("hwrng: core - Replace u32 in driver API with byte array") Cc: <stable@vger.kernel.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'drivers/char')
-rw-r--r--drivers/char/hw_random/core.c34
1 files changed, 21 insertions, 13 deletions
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;
+ } 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);
@@ -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: