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List: cygwin-patches
Subject: [PATCH] Cygwin: spawn: Fix segfalt when too many command line args are specified.
From: Takashi Yano <takashi.yano () nifty ! ne ! jp>
Date: 2023-08-28 9:20:12
Message-ID: 20230828092012.751-1-takashi.yano () nifty ! ne ! jp
[Download RAW message or body]
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, the total length of the arguments is restricted to
1/4 of total stack size for the process, and spawnve() returns E2BIG if
the size exceeds the limit.
Reported-by: Ed Morton <mortoneccc@comcast.net>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
---
winsup/cygwin/release/3.4.9 | 3 +++
winsup/cygwin/spawn.cc | 41 ++++++++++++++++++++++++++++++++++++-
winsup/cygwin/sysconf.cc | 9 +++++++-
3 files changed, 51 insertions(+), 2 deletions(-)
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..b38e4de27 100644
--- a/winsup/cygwin/spawn.cc
+++ b/winsup/cygwin/spawn.cc
@@ -284,6 +284,29 @@ extern "C" void __posix_spawn_sem_release (void *sem, int error);
extern DWORD mutex_timeout; /* defined in fhandler_termios.cc */
+static size_t
+get_stack_size (const WCHAR *filename)
+{
+ HANDLE h;
+ h = CreateFileW (filename, GENERIC_READ, FILE_SHARE_READ,
+ NULL, OPEN_EXISTING, 0, NULL);
+ char buf[1024];
+ DWORD n;
+ ReadFile (h, buf, sizeof (buf), &n, 0);
+ CloseHandle (h);
+ IMAGE_NT_HEADERS32 *p = (IMAGE_NT_HEADERS32 *) memmem (buf, n, "PE\0\0", 4);
+ if (!p)
+ return 0;
+ if ((char *) &p->OptionalHeader.SizeOfStackCommit > buf + n)
+ return 0; /* buf[] is not enough */
+ if (p->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR32_MAGIC)
+ return p->OptionalHeader.SizeOfStackReserve;
+ IMAGE_NT_HEADERS64 *p64 = (IMAGE_NT_HEADERS64 *) p;
+ if ((char *) &p64->OptionalHeader.SizeOfStackCommit > buf + n)
+ return 0; /* buf[] is not enough */
+ return p64->OptionalHeader.SizeOfStackReserve;
+}
+
int
child_info_spawn::worker (const char *prog_arg, const char *const *argv,
const char *const envp[], int mode,
@@ -351,8 +374,9 @@ 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;
@@ -621,6 +645,21 @@ child_info_spawn::worker (const char *prog_arg, const char *const *argv,
}
}
+ if (iscygwin ())
+ {
+ size_t child_stack_size = get_stack_size (runpath);
+ /* char *argv[] will be placed on the stack in dll_crt0_1(), so
+ restrict total argument length to 1/4 of total stack size. */
+ bool too_many_args = child_stack_size ?
+ arg_len > child_stack_size / 4 : ac >= MAXWINCMDLEN;
+ if (too_many_args)
+ {
+ set_errno (E2BIG);
+ res = -1;
+ __leave;
+ }
+ }
+
bool no_pcon = mode != _P_OVERLAY && mode != _P_WAIT;
term_spawn_worker.setup (iscygwin (), handle (fileno_stdin, false),
runpath, no_pcon, reset_sendsig, envblock);
diff --git a/winsup/cygwin/sysconf.cc b/winsup/cygwin/sysconf.cc
index 2db92e4de..6cb2aecd0 100644
--- a/winsup/cygwin/sysconf.cc
+++ b/winsup/cygwin/sysconf.cc
@@ -21,6 +21,13 @@ details. */
#include "cpuid.h"
#include "clock.h"
+#define DEFAULT_STACKGUARD (wincap.def_guard_page_size() + wincap.page_size ())
+static long
+get_arg_max (int in)
+{
+ return (long) (get_rlimit_stack () + DEFAULT_STACKGUARD) / 4;
+}
+
static long
get_page_size (int in)
{
@@ -485,7 +492,7 @@ static struct
};
} sca[] =
{
- {cons, {c:ARG_MAX}}, /* 0, _SC_ARG_MAX */
+ {func, {f:get_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 */
--
2.39.0
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