uaccess: Selectively open read or write user access

When opening user access to only perform reads, only open read access.
When opening user access to only perform writes, only open write
access.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2e73bc57125c2c6ab12a587586a4eed3a47105fc.1585898438.git.christophe.leroy@c-s.fr

fs/readdir.c

@@ -242,7 +242,7 @@ static int filldir(struct dir_context *ctx, const char *name, int namlen,
 		return -EINTR;
 	dirent = buf->current_dir;
 	prev = (void __user *) dirent - prev_reclen;
-	if (!user_access_begin(prev, reclen + prev_reclen))
+	if (!user_write_access_begin(prev, reclen + prev_reclen))
 		goto efault;
 
 	/* This might be 'dirent->d_off', but if so it will get overwritten */
@@ -251,14 +251,14 @@ static int filldir(struct dir_context *ctx, const char *name, int namlen,
 	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 	unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
 	unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
-	user_access_end();
+	user_write_access_end();
 
 	buf->current_dir = (void __user *)dirent + reclen;
 	buf->prev_reclen = reclen;
 	buf->count -= reclen;
 	return 0;
 efault_end:
-	user_access_end();
+	user_write_access_end();
 efault:
 	buf->error = -EFAULT;
 	return -EFAULT;
@@ -327,7 +327,7 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 		return -EINTR;
 	dirent = buf->current_dir;
 	prev = (void __user *)dirent - prev_reclen;
-	if (!user_access_begin(prev, reclen + prev_reclen))
+	if (!user_write_access_begin(prev, reclen + prev_reclen))
 		goto efault;
 
 	/* This might be 'dirent->d_off', but if so it will get overwritten */
@@ -336,7 +336,7 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 	unsafe_put_user(d_type, &dirent->d_type, efault_end);
 	unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
-	user_access_end();
+	user_write_access_end();
 
 	buf->prev_reclen = reclen;
 	buf->current_dir = (void __user *)dirent + reclen;
@@ -344,7 +344,7 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 	return 0;
 
 efault_end:
-	user_access_end();
+	user_write_access_end();
 efault:
 	buf->error = -EFAULT;
 	return -EFAULT;

kernel/compat.c

@@ -199,7 +199,7 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
 	bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
 	nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
 
-	if (!user_access_begin(umask, bitmap_size / 8))
+	if (!user_read_access_begin(umask, bitmap_size / 8))
 		return -EFAULT;
 
 	while (nr_compat_longs > 1) {
@@ -211,11 +211,11 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
 	}
 	if (nr_compat_longs)
 		unsafe_get_user(*mask, umask++, Efault);
-	user_access_end();
+	user_read_access_end();
 	return 0;
 
 Efault:
-	user_access_end();
+	user_read_access_end();
 	return -EFAULT;
 }
 
@@ -228,7 +228,7 @@ long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
 	bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
 	nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
 
-	if (!user_access_begin(umask, bitmap_size / 8))
+	if (!user_write_access_begin(umask, bitmap_size / 8))
 		return -EFAULT;
 
 	while (nr_compat_longs > 1) {
@@ -239,10 +239,10 @@ long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
 	}
 	if (nr_compat_longs)
 		unsafe_put_user((compat_ulong_t)*mask, umask++, Efault);
-	user_access_end();
+	user_write_access_end();
 	return 0;
 Efault:
-	user_access_end();
+	user_write_access_end();
 	return -EFAULT;
 }
 

kernel/exit.c

@@ -1557,7 +1557,7 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
 	if (!infop)
 		return err;
 
-	if (!user_access_begin(infop, sizeof(*infop)))
+	if (!user_write_access_begin(infop, sizeof(*infop)))
 		return -EFAULT;
 
 	unsafe_put_user(signo, &infop->si_signo, Efault);
@@ -1566,10 +1566,10 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
 	unsafe_put_user(info.pid, &infop->si_pid, Efault);
 	unsafe_put_user(info.uid, &infop->si_uid, Efault);
 	unsafe_put_user(info.status, &infop->si_status, Efault);
-	user_access_end();
+	user_write_access_end();
 	return err;
 Efault:
-	user_access_end();
+	user_write_access_end();
 	return -EFAULT;
 }
 
@@ -1684,7 +1684,7 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 	if (!infop)
 		return err;
 
-	if (!user_access_begin(infop, sizeof(*infop)))
+	if (!user_write_access_begin(infop, sizeof(*infop)))
 		return -EFAULT;
 
 	unsafe_put_user(signo, &infop->si_signo, Efault);
@@ -1693,10 +1693,10 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 	unsafe_put_user(info.pid, &infop->si_pid, Efault);
 	unsafe_put_user(info.uid, &infop->si_uid, Efault);
 	unsafe_put_user(info.status, &infop->si_status, Efault);
-	user_access_end();
+	user_write_access_end();
 	return err;
 Efault:
-	user_access_end();
+	user_write_access_end();
 	return -EFAULT;
 }
 #endif

lib/strncpy_from_user.c

@@ -116,9 +116,9 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
 
 		kasan_check_write(dst, count);
 		check_object_size(dst, count, false);
-		if (user_access_begin(src, max)) {
+		if (user_read_access_begin(src, max)) {
 			retval = do_strncpy_from_user(dst, src, count, max);
-			user_access_end();
+			user_read_access_end();
 			return retval;
 		}
 	}

lib/strnlen_user.c

@@ -109,9 +109,9 @@ long strnlen_user(const char __user *str, long count)
 		if (max > count)
 			max = count;
 
-		if (user_access_begin(str, max)) {
+		if (user_read_access_begin(str, max)) {
 			retval = do_strnlen_user(str, count, max);
-			user_access_end();
+			user_read_access_end();
 			return retval;
 		}
 	}

lib/usercopy.c

@@ -58,7 +58,7 @@ int check_zeroed_user(const void __user *from, size_t size)
 	from -= align;
 	size += align;
 
-	if (!user_access_begin(from, size))
+	if (!user_read_access_begin(from, size))
 		return -EFAULT;
 
 	unsafe_get_user(val, (unsigned long __user *) from, err_fault);
@@ -79,10 +79,10 @@ int check_zeroed_user(const void __user *from, size_t size)
 		val &= aligned_byte_mask(size);
 
 done:
-	user_access_end();
+	user_read_access_end();
 	return (val == 0);
 err_fault:
-	user_access_end();
+	user_read_access_end();
 	return -EFAULT;
 }
 EXPORT_SYMBOL(check_zeroed_user);