From: Herbert Xu herbert@gondor.apana.org.au

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@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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org (cherry picked from commit eafd83b92f6c044007a3591cbd476bcf90455990) Signed-off-by: Vegard Nossum vegard.nossum@oracle.com (cherry picked from commit 581445afd04cac92963d8b56b3eea08b320d6330)

Orabug: 36806668 CVE: CVE-2023-52615

Signed-off-by: Harshit Mogalapalli harshit.m.mogalapalli@oracle.com Reviewed-by: Saeed Mirzamohammadi saeed.mirzamohammadi@oracle.com

Conflicts: drivers/char/hw_random/core.c -- Minor contextual conflicts due to missing commit: affdec58dafc ("hwrng: core - Replace asm/uaccess.h by linux/uaccess.h") in UEK4, and it is not a candidate for backporting, so resolved conflicts instead

Signed-off-by: Alok Tiwari alok.a.tiwari@oracle.com --- drivers/char/hw_random/core.c | 34 +++++++++++++++++++++------------- 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 5643b65cee20..208d0fc2c923 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -43,6 +43,7 @@ #include <linux/slab.h> #include <linux/random.h> #include <linux/err.h> +#include <linux/string.h> #include <asm/uaccess.h>

@@ -51,6 +52,8 @@ #define RNG_MISCDEV_MINOR 183 /* official */

+#define RNG_BUFFER_SIZE (SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES) + static struct hwrng *current_rng; static struct task_struct *hwrng_fill; static LIST_HEAD(rng_list); @@ -79,7 +82,7 @@ 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) @@ -222,6 +225,7 @@ 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; @@ -246,34 +250,37 @@ 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); @@ -284,6 +291,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, } } out: + memzero_explicit(buffer, sizeof(buffer)); return ret ? : err;

out_unlock_reading: