| Message ID | ZWqCAsCUGN1cFIIT@gondor.apana.org.au (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | hwrng: core - Fix page fault dead lock on mmap-ed hwrng | expand |
On Sat, 2 Dec 2023 at 08:05, Herbert Xu <herbert@gondor.apana.org.au> wrote: > > 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> > > 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@gondor.apana.org.au> > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt > Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com> Regards, PrasannaKumar
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:
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>