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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.
This commit is contained in:
Michael Haubenwallner 2017-03-10 11:32:54 +01:00 committed by Corinna Vinschen
parent 22d68bada3
commit 3956ddd9bf
1 changed files with 48 additions and 24 deletions
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72
winsup/cygwin/forkable.cc
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@ -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 */
return false;
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 ret;
}
/* return the number of characters necessary to store one forkable name */