https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=3956ddd9bf28c518e73faf74c812379de02c3881
commit 3956ddd9bf28c518e73faf74c812379de02c3881
Author: Michael Haubenwallner <michael.haubenwall...@ssi-schaefer.com>
Date: Fri Mar 10 11:32:54 2017 +0100
forkables: hardlink without WRITE_ATTRIBUTES first
When the current process has renamed (to bin) a readonly dll, we get
STATUS_TRANSACTION_NOT_ACTIVE for unknown reason when subsequently
creating the forkable hardlink. A workaround is to open the original
file with FILE_WRITE_ATTRIBUTES access, but that fails with permission
denied for users not owning the original file.
* forkable.cc (dll::create_forkable): Retry hardlink creation using the
original file's handle opened with FILE_WRITE_ATTRIBUTES access when the
first attempt fails with STATUS_TRANSACTION_NOT_ACTIVE.
Diff:
---
winsup/cygwin/forkable.cc | 72 +++++++++++++++++++++++++++++++----------------
1 file changed, 48 insertions(+), 24 deletions(-)
diff --git a/winsup/cygwin/forkable.cc b/winsup/cygwin/forkable.cc
index 1e02a8a..1067eac 100644
--- a/winsup/cygwin/forkable.cc
+++ b/winsup/cygwin/forkable.cc
@@ -423,7 +423,14 @@ dll::nominate_forkable (PCWCHAR dirx_name)
}
/* Create the nominated hardlink for one indivitual dll,
- inside another subdirectory when dynamically loaded. */
+ inside another subdirectory when dynamically loaded.
+
+ We've not found a performant way yet to protect fork against
+ updates to main executables and/or dlls that do not reside on
+ the same NTFS filesystem as the <cygroot>/var/run/cygfork/
+ directory. But as long as the main executable can be hardlinked,
+ dll redirection works for any other hardlink-able dll, while
+ non-hardlink-able dlls are used from their original location. */
bool
dll::create_forkable ()
{
@@ -465,14 +472,6 @@ dll::create_forkable ()
if (devhandle == INVALID_HANDLE_VALUE)
return false; /* impossible */
- HANDLE fh = dll_list::ntopenfile ((PCWCHAR)&fii.IndexNumber, NULL,
- FILE_OPEN_BY_FILE_ID,
- FILE_WRITE_ATTRIBUTES,
- devhandle);
- NtClose (devhandle);
- if (fh == INVALID_HANDLE_VALUE)
- return false; /* impossible */
-
int ntlen = wcslen (ntname);
int bufsize = sizeof (FILE_LINK_INFORMATION) + ntlen * sizeof (*ntname);
PFILE_LINK_INFORMATION pfli = (PFILE_LINK_INFORMATION) alloca (bufsize);
@@ -483,22 +482,47 @@ dll::create_forkable ()
pfli->ReplaceIfExists = FALSE; /* allow concurrency */
pfli->RootDirectory = NULL;
- IO_STATUS_BLOCK iosb;
- NTSTATUS status = NtSetInformationFile (fh, &iosb, pfli, bufsize,
- FileLinkInformation);
- NtClose (fh);
- debug_printf ("%y = NtSetInformationFile (%p, FileLink %W, iosb.Status %y)",
- status, fh, pfli->FileName, iosb.Status);
- if (NT_SUCCESS (status) || status == STATUS_OBJECT_NAME_COLLISION)
- /* We've not found a performant way yet to protect fork against updates
- to main executables and/or dlls that do not reside on the same NTFS
- filesystem as the <cygroot>/var/run/cygfork/ directory.
- But as long as the main executable can be hardlinked, dll redirection
- works for any other hardlink-able dll, while non-hardlink-able dlls
- are used from their original location. */
- return true;
+ /* When we get STATUS_TRANSACTION_NOT_ACTIVE from hardlink creation,
+ the current process has renamed the file while it had the readonly
+ attribute. The rename() function uses a transaction for combined
+ writeable+rename action if possible to provide atomicity.
+ Although the transaction is closed afterwards, creating a hardlink
+ for this file requires the FILE_WRITE_ATTRIBUTES access, for unknown
+ reason. On the other hand, always requesting FILE_WRITE_ATTRIBUTES
+ would fail for users that do not own the original file. */
+ bool ret = false;
+ int access = 0; /* first attempt */
+ while (true)
+ {
+ HANDLE fh = dll_list::ntopenfile ((PCWCHAR)&fii.IndexNumber, NULL,
+ FILE_OPEN_BY_FILE_ID,
+ access,
+ devhandle);
+ if (fh == INVALID_HANDLE_VALUE)
+ break; /* impossible */
+
+ IO_STATUS_BLOCK iosb;
+ NTSTATUS status = NtSetInformationFile (fh, &iosb, pfli, bufsize,
+ FileLinkInformation);
+ NtClose (fh);
+ debug_printf ("%y = NtSetInformationFile (%p, FileLink %W, iosb.Status
%y)",
+ status, fh, pfli->FileName, iosb.Status);
+ if (NT_SUCCESS (status) || status == STATUS_OBJECT_NAME_COLLISION)
+ {
+ ret = true;
+ break;
+ }
+
+ if (status != STATUS_TRANSACTION_NOT_ACTIVE ||
+ access == FILE_WRITE_ATTRIBUTES)
+ break;
+
+ access = FILE_WRITE_ATTRIBUTES; /* second attempt */
+ }
+
+ NtClose (devhandle);
- return false;
+ return ret;
}
/* return the number of characters necessary to store one forkable name */
