fs: move permission hook out of do_iter_write()

In many of the vfs helpers, the rw_verity_area() checks are called before
taking sb_start_write(), making them "start-write-safe".
do_iter_write() is an exception to this rule.

do_iter_write() has two callers - vfs_iter_write() and vfs_writev().
Move rw_verify_area() and other checks from do_iter_write() out to
its callers to make them "start-write-safe".

Move also the fsnotify_modify() hook to align with similar pattern
used in vfs_write() and other vfs helpers.

This is needed for fanotify "pre content" events.

Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20231122122715.2561213-12-amir73il@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/read_write.c b/fs/read_write.c
index 3aa3bce18075fa1c965d0107c52e8de242365f96..d08d0a3ff7dec72a6e7ca1e2d79a2391f6e18797 100644 (file)
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -838,33 +838,6 @@ ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos,
 }
 EXPORT_SYMBOL(vfs_iter_read);
 
-static ssize_t do_iter_write(struct file *file, struct iov_iter *iter,
-                            loff_t *pos, rwf_t flags)
-{
-       size_t tot_len;
-       ssize_t ret = 0;
-
-       if (!(file->f_mode & FMODE_WRITE))
-               return -EBADF;
-       if (!(file->f_mode & FMODE_CAN_WRITE))
-               return -EINVAL;
-
-       tot_len = iov_iter_count(iter);
-       if (!tot_len)
-               return 0;
-       ret = rw_verify_area(WRITE, file, pos, tot_len);
-       if (ret < 0)
-               return ret;
-
-       if (file->f_op->write_iter)
-               ret = do_iter_readv_writev(file, iter, pos, WRITE, flags);
-       else
-               ret = do_loop_readv_writev(file, iter, pos, WRITE, flags);
-       if (ret > 0)
-               fsnotify_modify(file);
-       return ret;
-}
-
 ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
                            struct iov_iter *iter)
 {
@@ -896,13 +869,28 @@ EXPORT_SYMBOL(vfs_iocb_iter_write);
 ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos,
                       rwf_t flags)
 {
-       int ret;
+       size_t tot_len;
+       ssize_t ret;
 
+       if (!(file->f_mode & FMODE_WRITE))
+               return -EBADF;
+       if (!(file->f_mode & FMODE_CAN_WRITE))
+               return -EINVAL;
        if (!file->f_op->write_iter)
                return -EINVAL;
 
+       tot_len = iov_iter_count(iter);
+       if (!tot_len)
+               return 0;
+
+       ret = rw_verify_area(WRITE, file, ppos, tot_len);
+       if (ret < 0)
+               return ret;
+
        file_start_write(file);
-       ret = do_iter_write(file, iter, ppos, flags);
+       ret = do_iter_readv_writev(file, iter, ppos, WRITE, flags);
+       if (ret > 0)
+               fsnotify_modify(file);
        file_end_write(file);
 
        return ret;
@@ -927,20 +915,42 @@ static ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
 }
 
 static ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
-                  unsigned long vlen, loff_t *pos, rwf_t flags)
+                         unsigned long vlen, loff_t *pos, rwf_t flags)
 {
        struct iovec iovstack[UIO_FASTIOV];
        struct iovec *iov = iovstack;
        struct iov_iter iter;
-       ssize_t ret;
+       size_t tot_len;
+       ssize_t ret = 0;
 
-       ret = import_iovec(ITER_SOURCE, vec, vlen, ARRAY_SIZE(iovstack), &iov, &iter);
-       if (ret >= 0) {
-               file_start_write(file);
-               ret = do_iter_write(file, &iter, pos, flags);
-               file_end_write(file);
-               kfree(iov);
-       }
+       if (!(file->f_mode & FMODE_WRITE))
+               return -EBADF;
+       if (!(file->f_mode & FMODE_CAN_WRITE))
+               return -EINVAL;
+
+       ret = import_iovec(ITER_SOURCE, vec, vlen, ARRAY_SIZE(iovstack), &iov,
+                          &iter);
+       if (ret < 0)
+               return ret;
+
+       tot_len = iov_iter_count(&iter);
+       if (!tot_len)
+               goto out;
+
+       ret = rw_verify_area(WRITE, file, pos, tot_len);
+       if (ret < 0)
+               goto out;
+
+       file_start_write(file);
+       if (file->f_op->write_iter)
+               ret = do_iter_readv_writev(file, &iter, pos, WRITE, flags);
+       else
+               ret = do_loop_readv_writev(file, &iter, pos, WRITE, flags);
+       if (ret > 0)
+               fsnotify_modify(file);
+       file_end_write(file);
+out:
+       kfree(iov);
        return ret;
 }