commit 06bbaa6dc53cb72040db952053432541acb9adc7
author Al Viro <viro@zeniv.linux.org.uk> Mon Sep 26 11:59:14 2022 -0400
committer Al Viro <viro@zeniv.linux.org.uk> Wed Sep 28 14:28:40 2022 -0400
tree 113842569565963748044a4b00498e31051a68c1
parent bfbfb6182ad1d7d184b16f25165faad879147f79

[coredump] don't use __kernel_write() on kmap_local_page()

passing kmap_local_page() result to __kernel_write() is unsafe -
random ->write_iter() might (and 9p one does) get unhappy when
passed ITER_KVEC with pointer that came from kmap_local_page().

Fix by providing a variant of __kernel_write() that takes an iov_iter
from caller (__kernel_write() becomes a trivial wrapper) and adding
dump_emit_page() that parallels dump_emit(), except that instead of
__kernel_write() it uses __kernel_write_iter() with ITER_BVEC source.

Fixes: 3159ed57792b "fs/coredump: use kmap_local_page()"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/internal.h

diff --git a/fs/internal.h b/fs/internal.h
index 87e96b9..3e206d3 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -16,6 +16,7 @@ struct shrink_control;
 struct fs_context;
 struct user_namespace;
 struct pipe_inode_info;
+struct iov_iter;
 
 /*
  * block/bdev.c
@@ -221,3 +222,5 @@ ssize_t do_getxattr(struct user_namespace *mnt_userns,
 int setxattr_copy(const char __user *name, struct xattr_ctx *ctx);
 int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 		struct xattr_ctx *ctx);
+
+ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos);