[PATCH] iov_iter: fix copy_page_to_iter_nofault()

[PATCH] iov_iter: fix copy_page_to_iter_nofault()

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

The recent conversion to inline functions made two mistakes:

1. It tries to copy the full amount requested (bytes), not just what's
   available in the kmap'd page (n).
2. It's not applying the offset in the first page.

Note that copy_page_to_iter_nofault() is only used by /proc/kcore. This
was detected by drgn's test suite.

Fixes: f1982740f5e7 ("iov_iter: Convert iterate*() to inline funcs")
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 lib/iov_iter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index de7d11cf4c63..8ff6824a1005 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -409,7 +409,7 @@ size_t copy_page_to_iter_nofault(struct page *page, unsigned offset, size_t byte
 		void *kaddr = kmap_local_page(page);
 		size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
 
-		n = iterate_and_advance(i, bytes, kaddr,
+		n = iterate_and_advance(i, n, kaddr + offset,
 					copy_to_user_iter_nofault,
 					memcpy_to_iter);
 		kunmap_local(kaddr);
-- 
2.42.0

Re: [PATCH] iov_iter: fix copy_page_to_iter_nofault()

[Christian Brauner]

On Fri, 17 Nov 2023 13:38:46 -0800, Omar Sandoval wrote:
> The recent conversion to inline functions made two mistakes:
> 
> 1. It tries to copy the full amount requested (bytes), not just what's
>    available in the kmap'd page (n).
> 2. It's not applying the offset in the first page.
> 
> Note that copy_page_to_iter_nofault() is only used by /proc/kcore. This
> was detected by drgn's test suite.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] iov_iter: fix copy_page_to_iter_nofault()
      https://git.kernel.org/vfs/vfs/c/e15912e71ae0

Re: [PATCH] iov_iter: fix copy_page_to_iter_nofault()

[David Howells]

Omar Sandoval <osandov@osandov.com> wrote:

> From: Omar Sandoval <osandov@fb.com>
> 
> The recent conversion to inline functions made two mistakes:
> 
> 1. It tries to copy the full amount requested (bytes), not just what's
>    available in the kmap'd page (n).
> 2. It's not applying the offset in the first page.
> 
> Note that copy_page_to_iter_nofault() is only used by /proc/kcore. This
> was detected by drgn's test suite.
> 
> Fixes: f1982740f5e7 ("iov_iter: Convert iterate*() to inline funcs")
> Signed-off-by: Omar Sandoval <osandov@fb.com>

Acked-by: David Howells <dhowells@redhat.com>