[newlib-cygwin] Cygwin: Fix segfalt when too many command line args are specified.

Takashi Yano tyan0@sourceware.org
Mon Aug 28 16:00:00 GMT 2023


https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=44f73c5a620689d6821c4bd0444051be57f8251a

commit 44f73c5a620689d6821c4bd0444051be57f8251a
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Mon Aug 28 22:14:41 2023 +0900

    Cygwin: Fix segfalt when too many command line args are specified.
    
    Previously, the number of command line args was not checked for
    cygwin process. Due to this, segmentation fault was caused if too
    many command line args are specified.
    https://cygwin.com/pipermail/cygwin/2023-August/254333.html
    
    Since char *argv[argc + 1] is placed on the stack in dll_crt0_1(),
    STATUS_STACK_OVERFLOW occurs if the stack does not have enough
    space.
    
    With this patch, char *argv[] is placed in heap instead of stack
    and ARG_MAX is increased from 32000 to 2097152 which is default
    value of Linux. The argument length is also compared with ARG_MAX
    and spawnve() returns E2BIG if it is too long.
    
    Reported-by: Ed Morton
    Reviewed-by: Corinna Vinschen <corinna@vinschen.de>
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

Diff:
---
 winsup/cygwin/dcrt0.cc                | 7 ++-----
 winsup/cygwin/local_includes/winsup.h | 4 ++++
 winsup/cygwin/release/3.4.9           | 3 +++
 winsup/cygwin/spawn.cc                | 9 ++++++++-
 winsup/cygwin/sysconf.cc              | 2 +-
 5 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/winsup/cygwin/dcrt0.cc b/winsup/cygwin/dcrt0.cc
index 49b7a44ae..1d8810546 100644
--- a/winsup/cygwin/dcrt0.cc
+++ b/winsup/cygwin/dcrt0.cc
@@ -978,11 +978,8 @@ dll_crt0_1 (void *)
 	 a change to an element of argv[] it does not affect Cygwin's argv.
 	 Changing the the contents of what argv[n] points to will still
 	 affect Cygwin.  This is similar (but not exactly like) Linux. */
-      char *newargv[__argc + 1];
-      char **nav = newargv;
-      char **oav = __argv;
-      while ((*nav++ = *oav++) != NULL)
-	continue;
+      char **newargv = (char **) malloc ((__argc + 1) * sizeof (char *));
+      memcpy (newargv, __argv, (__argc + 1) * sizeof (char *));
       /* Handle any signals which may have arrived */
       sig_dispatch_pending (false);
       _my_tls.call_signal_handler ();
diff --git a/winsup/cygwin/local_includes/winsup.h b/winsup/cygwin/local_includes/winsup.h
index c9788de8f..57bd38c9f 100644
--- a/winsup/cygwin/local_includes/winsup.h
+++ b/winsup/cygwin/local_includes/winsup.h
@@ -73,6 +73,10 @@ uint32_t cygwin_inet_addr (const char *cp);
    application provided path strings we handle. */
 #define NT_MAX_PATH 32768
 
+/* CYG_ARG_MAX is the maximum total length of command line args.
+   The value 2097152 is the default ARG_MAX value in Linux. */
+#define CYG_ARG_MAX 2097152
+
 /* This definition allows to define wide char strings using macros as
    parameters.  See the definition of __CONCAT in newlib's sys/cdefs.h
    and accompanying comment. */
diff --git a/winsup/cygwin/release/3.4.9 b/winsup/cygwin/release/3.4.9
index 2f2da9e13..53c4e5fc8 100644
--- a/winsup/cygwin/release/3.4.9
+++ b/winsup/cygwin/release/3.4.9
@@ -8,3 +8,6 @@ Bug Fixes
 - For the time being, disable creating special files using mknod/mkfifo
   on NFS.
   Addresses: https://cygwin.com/pipermail/cygwin/2023-August/254266.html
+
+- Fix segfault when too many command line args are specified.
+  Addresses: https://cygwin.com/pipermail/cygwin/2023-August/254333.html
diff --git a/winsup/cygwin/spawn.cc b/winsup/cygwin/spawn.cc
index c16fe269a..c4f116728 100644
--- a/winsup/cygwin/spawn.cc
+++ b/winsup/cygwin/spawn.cc
@@ -351,8 +351,9 @@ child_info_spawn::worker (const char *prog_arg, const char *const *argv,
 	 We need to quote any argument that has whitespace or embedded "'s.  */
 
       int ac;
+      size_t arg_len = 0;
       for (ac = 0; argv[ac]; ac++)
-	/* nothing */;
+	arg_len += strlen (argv[ac]) + 1;
 
       int err;
       const char *ext;
@@ -521,6 +522,12 @@ child_info_spawn::worker (const char *prog_arg, const char *const *argv,
 	  __leave;
 	}
       set (chtype, real_path.iscygexec ());
+      if (iscygwin () && arg_len > (size_t) sysconf (_SC_ARG_MAX))
+	{
+	  set_errno (E2BIG);
+	  res = -1;
+	  __leave;
+	}
       __stdin = in__stdin;
       __stdout = in__stdout;
       record_children ();
diff --git a/winsup/cygwin/sysconf.cc b/winsup/cygwin/sysconf.cc
index 2db92e4de..7cdfbdb9d 100644
--- a/winsup/cygwin/sysconf.cc
+++ b/winsup/cygwin/sysconf.cc
@@ -485,7 +485,7 @@ static struct
     };
 } sca[] =
 {
-  {cons, {c:ARG_MAX}},			/*   0, _SC_ARG_MAX */
+  {cons, {c:CYG_ARG_MAX}},		/*   0, _SC_ARG_MAX */
   {cons, {c:CHILD_MAX}},		/*   1, _SC_CHILD_MAX */
   {cons, {c:CLOCKS_PER_SEC}},		/*   2, _SC_CLK_TCK */
   {cons, {c:NGROUPS_MAX}},		/*   3, _SC_NGROUPS_MAX */


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