Missing CAMLparam in win32's Unix.stat (#11737)

mlasson · nojb · commit 6729eb8a1057 · 2022-11-21T09:05:33.000+01:00
The `path` argument is used after a `caml_enter_blocking_section` when the path does not exists (the path is used to build the unix error exception). Unfortunately, during the blocking section we may "yield" to a thread that can trigger a garbage collection and move the content of `path` elsewhere, triggering a segfault. The CAMLparam is therefore needed in that case. (cherry picked from commit 3d8fb96)
diff --git a/Changes b/Changes
@@ -64,6 +64,10 @@ OCaml 4.14 maintenance branch
   mismatch error involving recursive types.
   (Florian Angeletti, review by Gabriel Scherer)
 
+- #11737: Fix segfault condition in Unix.stat under Windows in the presence of
+  multiple threads.
+  (Marc Lasson, Nicolás Ojeda Bär, review by Gabriel Scherer and David Allsopp)
+
 OCaml 4.14.0 (28 March 2022)
 ----------------------------
 
diff --git a/otherlibs/win32unix/stat.c b/otherlibs/win32unix/stat.c
@@ -347,50 +347,54 @@ static int do_stat(int do_lstat, int use_64, const char* opath, HANDLE fstat, __
 
 CAMLprim value unix_stat(value path)
 {
+  CAMLparam1(path);
   struct _stat64 buf;
   __int64 st_ino;
 
   caml_unix_check_path(path, "stat");
   if (!do_stat(0, 0, String_val(path), NULL, &st_ino, &buf)) {
     uerror("stat", path);
   }
-  return stat_aux(0, st_ino, &buf);
+  CAMLreturn (stat_aux(0, st_ino, &buf));
 }
 
 CAMLprim value unix_stat_64(value path)
 {
+  CAMLparam1(path);
   struct _stat64 buf;
   __int64 st_ino;
 
   caml_unix_check_path(path, "stat");
   if (!do_stat(0, 1, String_val(path), NULL, &st_ino, &buf)) {
     uerror("stat", path);
   }
-  return stat_aux(1, st_ino, &buf);
+  CAMLreturn (stat_aux(1, st_ino, &buf));
 }
 
 CAMLprim value unix_lstat(value path)
 {
+  CAMLparam1(path);
   struct _stat64 buf;
   __int64 st_ino;
 
   caml_unix_check_path(path, "lstat");
   if (!do_stat(1, 0, String_val(path), NULL, &st_ino, &buf)) {
     uerror("lstat", path);
   }
-  return stat_aux(0, st_ino, &buf);
+  CAMLreturn (stat_aux(0, st_ino, &buf));
 }
 
 CAMLprim value unix_lstat_64(value path)
 {
+  CAMLparam1(path);
   struct _stat64 buf;
   __int64 st_ino;
 
   caml_unix_check_path(path, "lstat");
   if (!do_stat(1, 1, String_val(path), NULL, &st_ino, &buf)) {
     uerror("lstat", path);
   }
-  return stat_aux(1, st_ino, &buf);
+  CAMLreturn (stat_aux(1, st_ino, &buf));
 }
 
 static value do_fstat(value handle, int use_64)

Original file line number	Diff line number	Diff line change
`@@ -347,50 +347,54 @@ static int do_stat(int do_lstat, int use_64, const char* opath, HANDLE fstat, __`
`347`	`347`
`348`	`348`	`CAMLprim value unix_stat(value path)`
`349`	`349`	`{`
	`350`	`+ CAMLparam1(path);`
`350`	`351`	`struct _stat64 buf;`
`351`	`352`	`__int64 st_ino;`
`352`	`353`
`353`	`354`	`caml_unix_check_path(path, "stat");`
`354`	`355`	`if (!do_stat(0, 0, String_val(path), NULL, &st_ino, &buf)) {`
`355`	`356`	`uerror("stat", path);`
`356`	`357`	`}`
`357`		`- return stat_aux(0, st_ino, &buf);`
	`358`	`+ CAMLreturn (stat_aux(0, st_ino, &buf));`
`358`	`359`	`}`
`359`	`360`
`360`	`361`	`CAMLprim value unix_stat_64(value path)`
`361`	`362`	`{`
	`363`	`+ CAMLparam1(path);`
`362`	`364`	`struct _stat64 buf;`
`363`	`365`	`__int64 st_ino;`
`364`	`366`
`365`	`367`	`caml_unix_check_path(path, "stat");`
`366`	`368`	`if (!do_stat(0, 1, String_val(path), NULL, &st_ino, &buf)) {`
`367`	`369`	`uerror("stat", path);`
`368`	`370`	`}`
`369`		`- return stat_aux(1, st_ino, &buf);`
	`371`	`+ CAMLreturn (stat_aux(1, st_ino, &buf));`
`370`	`372`	`}`
`371`	`373`
`372`	`374`	`CAMLprim value unix_lstat(value path)`
`373`	`375`	`{`
	`376`	`+ CAMLparam1(path);`
`374`	`377`	`struct _stat64 buf;`
`375`	`378`	`__int64 st_ino;`
`376`	`379`
`377`	`380`	`caml_unix_check_path(path, "lstat");`
`378`	`381`	`if (!do_stat(1, 0, String_val(path), NULL, &st_ino, &buf)) {`
`379`	`382`	`uerror("lstat", path);`
`380`	`383`	`}`
`381`		`- return stat_aux(0, st_ino, &buf);`
	`384`	`+ CAMLreturn (stat_aux(0, st_ino, &buf));`
`382`	`385`	`}`
`383`	`386`
`384`	`387`	`CAMLprim value unix_lstat_64(value path)`
`385`	`388`	`{`
	`389`	`+ CAMLparam1(path);`
`386`	`390`	`struct _stat64 buf;`
`387`	`391`	`__int64 st_ino;`
`388`	`392`
`389`	`393`	`caml_unix_check_path(path, "lstat");`
`390`	`394`	`if (!do_stat(1, 1, String_val(path), NULL, &st_ino, &buf)) {`
`391`	`395`	`uerror("lstat", path);`
`392`	`396`	`}`
`393`		`- return stat_aux(1, st_ino, &buf);`
	`397`	`+ CAMLreturn (stat_aux(1, st_ino, &buf));`
`394`	`398`	`}`
`395`	`399`
`396`	`400`	`static value do_fstat(value handle, int use_64)`