[PATCH 10/15] fs: move permission hook out of do_iter_write()

Amir Goldstein
2023-11-14T15:33:17Z

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>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
fs/read_write.c | 76 ++++++++++++++++++++++++++++++-------------------
1 file changed, 46 insertions(+), 30 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 8cdc6e6a9639..d4891346d42e 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -848,28 +848,10 @@ 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);
+ return 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;
+ return do_loop_readv_writev(file, iter, pos, WRITE, flags);
}

ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
@@ -903,13 +885,28 @@ 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);
+ if (ret > 0)
+ fsnotify_modify(file);
file_end_write(file);

return ret;
@@ -934,20 +931,39 @@ 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);
+ ret = do_iter_write(file, &iter, pos, flags);
+ if (ret > 0)
+ fsnotify_modify(file);
+ file_end_write(file);
+out:
+ kfree(iov);
return ret;
}

--
2.34.1