On 29/04/2025 18:42, Jeremy Drake via Cygwin-patches wrote:
In the CCP_POSIX_TO_WIN_W path, when `from` is a device,
cygwin_conv_path would attempt to write to the `to` buffer before the
validation of the `size`. This resulted in an EFAULT error in the
common use-case of passing `to` as NULL and `size` as 0 to get the
required size of `to` for the conversion (as used in
This is clearly not what's wanted! Thanks for fixing this!
cygwin_create_path). Instead, set a boolean and write to `to`
after validation.
Fixes: 43f65cdd7dae ("* Makefile.in (DLL_OFILES): Add fhandler_procsys.o.")
Addresses: https://cygwin.com/pipermail/cygwin/2025-April/258068.html
Signed-off-by: Jeremy Drake <cyg...@jdrake.com>
---
winsup/cygwin/path.cc | 5 ++++-
winsup/cygwin/release/3.6.2 | 3 +++
2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index 7a08e978ad..d26f99ee7f 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -3911,6 +3911,7 @@ cygwin_conv_path (cygwin_conv_path_t what, const void
*from, void *to,
int how = what & CCP_CONVFLAGS_MASK;
what &= CCP_CONVTYPE_MASK;
int ret = -1;
+ bool prependglobalroot = false;
__try
{
@@ -4019,7 +4020,7 @@ cygwin_conv_path (cygwin_conv_path_t what, const void
*from, void *to,
{
/* Device name points to somewhere else in the NT namespace.
Use GLOBALROOT prefix to convert to Win32 path. */
- to = (void *) wcpcpy ((wchar_t *) to, ro_u_globalroot.Buffer);
+ prependglobalroot = true;
It seems like this could all be done in-place in .Buffer here, but I'm
going to defer to Corinna on if that's at all clearer...
lsiz += ro_u_globalroot.Length / sizeof (WCHAR);
}
/* TODO: Same ".\\" band-aid as in CCP_POSIX_TO_WIN_A case. */
@@ -4075,6 +4076,8 @@ cygwin_conv_path (cygwin_conv_path_t what, const void
*from, void *to,
stpcpy ((char *) to, buf);
break;
case CCP_POSIX_TO_WIN_W:
+ if (prependglobalroot)
+ to = (void *) wcpcpy ((PWCHAR) to, ro_u_globalroot.Buffer);
wcpcpy ((PWCHAR) to, path);
break;
}
diff --git a/winsup/cygwin/release/3.6.2 b/winsup/cygwin/release/3.6.2
index bceabcab34..de6eae13fc 100644
--- a/winsup/cygwin/release/3.6.2
+++ b/winsup/cygwin/release/3.6.2
@@ -13,3 +13,6 @@ Fixes:
- Fix setting DOS attributes on devices.
Addresse: https://cygwin.com/pipermail/cygwin/2025-April/257940.html
+
+- Fix cygwin_conv_path writing to 'to' pointer before size is checked.
+ Addresses: https://cygwin.com/pipermail/cygwin/2025-April/258068.html
Seems like this should also touch:
https://cygwin.com/cygwin-api/func-cygwin-conv-path.html
(source in winsup/doc/path.xml)
I'm not sure what the conventional language to use for this common
behaviour:
"If size is 0, (to is ignored|to can be NULL) and cygwin_conv_path just
returns the required buffer size in bytes" ?
