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close_on_exec multithreaded decompression issue (#1906751)

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This commit is contained in:
Vincent Mihalkovic 2020-12-16 17:28:06 +01:00
parent fef64163af
commit b6f15c7ac0
2 changed files with 208 additions and 1 deletions
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201
file-5.39-CLOEXEC.patch Normal file
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@ -0,0 +1,201 @@
diff --git a/ChangeLog b/ChangeLog
index d46caaa0d..41d6e99d9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2020-12-08 16:24 Christos Zoulas <christos@zoulas.com>
+
+ * fix multithreaded decompression file descriptor issue
+ by using close-on-exec (Denys Vlasenko)
+
2020-06-14 20:02 Christos Zoulas <christos@zoulas.com>
* release 5.39
diff --git a/configure.ac b/configure.ac
index 64c9f42e3..521dc12db 100644
--- a/configure.ac
+++ b/configure.ac
@@ -166,7 +166,7 @@ else
fi])
dnl Checks for functions
-AC_CHECK_FUNCS(strndup mkstemp mkostemp utimes utime wcwidth strtof newlocale uselocale freelocale memmem)
+AC_CHECK_FUNCS(strndup mkstemp mkostemp utimes utime wcwidth strtof newlocale uselocale freelocale memmem pipe2)
dnl Provide implementation of some required functions if necessary
AC_REPLACE_FUNCS(getopt_long asprintf vasprintf strlcpy strlcat getline ctime_r asctime_r localtime_r gmtime_r pread strcasestr fmtcheck dprintf)
diff --git a/src/compress.c b/src/compress.c
index cbc2ce19b..9f65e4fa1 100644
--- a/src/compress.c
+++ b/src/compress.c
@@ -35,7 +35,7 @@
#include "file.h"
#ifndef lint
-FILE_RCSID("@(#)$File: compress.c,v 1.127 2020/05/31 00:11:06 christos Exp $")
+FILE_RCSID("@(#)$File: compress.c,v 1.129 2020/12/08 21:26:00 christos Exp $")
#endif
#include "magic.h"
@@ -844,8 +844,23 @@ uncompressbuf(int fd, size_t bytes_max, size_t method, const unsigned char *old,
for (i = 0; i < __arraycount(fdp); i++)
fdp[i][0] = fdp[i][1] = -1;
- if ((fd == -1 && pipe(fdp[STDIN_FILENO]) == -1) ||
- pipe(fdp[STDOUT_FILENO]) == -1 || pipe(fdp[STDERR_FILENO]) == -1) {
+ /*
+ * There are multithreaded users who run magic_file()
+ * from dozens of threads. If two parallel magic_file() calls
+ * analyze two large compressed files, both will spawn
+ * an uncompressing child here, which writes out uncompressed data.
+ * We read some portion, then close the pipe, then waitpid() the child.
+ * If uncompressed data is larger, child shound get EPIPE and exit.
+ * However, with *parallel* calls OTHER child may unintentionally
+ * inherit pipe fds, thus keeping pipe open and making writes in
+ * our child block instead of failing with EPIPE!
+ * (For the bug to occur, two threads must mutually inherit their pipes,
+ * and both must have large outputs. Thus it happens not that often).
+ * To avoid this, be sure to create pipes with O_CLOEXEC.
+ */
+ if ((fd == -1 && file_pipe_closexec(fdp[STDIN_FILENO]) == -1) ||
+ file_pipe_closexec(fdp[STDOUT_FILENO]) == -1 ||
+ file_pipe_closexec(fdp[STDERR_FILENO]) == -1) {
closep(fdp[STDIN_FILENO]);
closep(fdp[STDOUT_FILENO]);
return makeerror(newch, n, "Cannot create pipe, %s",
@@ -876,16 +891,20 @@ uncompressbuf(int fd, size_t bytes_max, size_t method, const unsigned char *old,
if (fdp[STDIN_FILENO][1] > 2)
(void) close(fdp[STDIN_FILENO][1]);
}
+ file_clear_closexec(STDIN_FILENO);
+
///FIXME: if one of the fdp[i][j] is 0 or 1, this can bomb spectacularly
if (copydesc(STDOUT_FILENO, fdp[STDOUT_FILENO][1]))
(void) close(fdp[STDOUT_FILENO][1]);
if (fdp[STDOUT_FILENO][0] > 2)
(void) close(fdp[STDOUT_FILENO][0]);
+ file_clear_closexec(STDOUT_FILENO);
if (copydesc(STDERR_FILENO, fdp[STDERR_FILENO][1]))
(void) close(fdp[STDERR_FILENO][1]);
if (fdp[STDERR_FILENO][0] > 2)
(void) close(fdp[STDERR_FILENO][0]);
+ file_clear_closexec(STDERR_FILENO);
(void)execvp(compr[method].argv[0],
RCAST(char *const *, RCAST(intptr_t, compr[method].argv)));
diff --git a/src/file.h b/src/file.h
index f00e8010b..6c3900479 100644
--- a/src/file.h
+++ b/src/file.h
@@ -27,7 +27,7 @@
*/
/*
* file.h - definitions for file(1) program
- * @(#)$File: file.h,v 1.220 2020/06/08 17:38:27 christos Exp $
+ * @(#)$File: file.h,v 1.223 2020/12/08 21:26:00 christos Exp $
*/
#ifndef __file_h__
@@ -143,6 +143,14 @@
#define MAX(a,b) (((a) > (b)) ? (a) : (b))
#endif
+#ifndef O_CLOEXEC
+# define O_CLOEXEC 0
+#endif
+
+#ifndef FD_CLOEXEC
+# define FD_CLOEXEC 1
+#endif
+
#define FILE_BADSIZE CAST(size_t, ~0ul)
#define MAXDESC 64 /* max len of text description/MIME type */
#define MAXMIME 80 /* max len of text MIME type */
@@ -540,6 +548,8 @@ protected char * file_printable(char *, size_t, const char *, size_t);
protected int file_os2_apptype(struct magic_set *, const char *, const void *,
size_t);
#endif /* __EMX__ */
+protected int file_pipe_closexec(int *);
+protected int file_clear_closexec(int);
protected void buffer_init(struct buffer *, int, const struct stat *,
const void *, size_t);
diff --git a/src/funcs.c b/src/funcs.c
index ecbfa28c5..bcf9ddaae 100644
--- a/src/funcs.c
+++ b/src/funcs.c
@@ -27,7 +27,7 @@
#include "file.h"
#ifndef lint
-FILE_RCSID("@(#)$File: funcs.c,v 1.115 2020/02/20 15:50:20 christos Exp $")
+FILE_RCSID("@(#)$File: funcs.c,v 1.118 2020/12/08 21:26:00 christos Exp $")
#endif /* lint */
#include "magic.h"
@@ -36,6 +36,9 @@ FILE_RCSID("@(#)$File: funcs.c,v 1.117 2020/06/25 16:52:48 christos Exp $")
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
+#ifdef HAVE_UNISTD_H
+#include <unistd.h> /* for pipe2() */
+#endif
#if defined(HAVE_WCHAR_H)
#include <wchar.h>
#endif
@@ -784,3 +787,22 @@ file_print_guid(char *str, size_t len, const uint64_t *guid)
g->data4[2], g->data4[3], g->data4[4], g->data4[5],
g->data4[6], g->data4[7]);
}
+
+protected int
+file_pipe_closexec(int *fds)
+{
+#ifdef HAVE_PIPE2
+ return pipe2(fds, O_CLOEXEC);
+#else
+ if (pipe(fds) == -1)
+ return -1;
+ (void)fcntl(fds[0], F_SETFD, FD_CLOEXEC);
+ (void)fcntl(fds[1], F_SETFD, FD_CLOEXEC);
+ return 0;
+#endif
+}
+
+protected int
+file_clear_closexec(int fd) {
+ return fcntl(fd, F_SETFD, 0);
+}
diff --git a/src/magic.c b/src/magic.c
index 17a7077d8..89f4e16c0 100644
--- a/src/magic.c
+++ b/src/magic.c
@@ -33,7 +33,7 @@
#include "file.h"
#ifndef lint
-FILE_RCSID("@(#)$File: magic.c,v 1.112 2020/06/08 19:44:10 christos Exp $")
+FILE_RCSID("@(#)$File: magic.c,v 1.113 2020/12/08 21:26:00 christos Exp $")
#endif /* lint */
#include "magic.h"
@@ -436,7 +436,7 @@ file_or_fd(struct magic_set *ms, const char *inname, int fd)
_setmode(STDIN_FILENO, O_BINARY);
#endif
if (inname != NULL) {
- int flags = O_RDONLY|O_BINARY|O_NONBLOCK;
+ int flags = O_RDONLY|O_BINARY|O_NONBLOCK|O_CLOEXEC;
errno = 0;
if ((fd = open(inname, flags)) < 0) {
okstat = stat(inname, &sb) == 0;
@@ -460,6 +460,9 @@ file_or_fd(struct magic_set *ms, const char *inname, int fd)
rv = 0;
goto done;
}
+#if O_CLOEXEC == 0
+ (void)fcntl(fd, F_SETFD, FD_CLOEXEC);
+#endif
}
if (fd != -1) {

8
file.spec
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@ -15,7 +15,7 @@
Summary: A utility for determining file types
Name: file
Version: 5.39
Release: 3%{?dist}
Release: 4%{?dist}
License: BSD
Source0: ftp://ftp.astron.com/pub/file/file-%{version}.tar.gz
@ -26,6 +26,9 @@ Patch0: file-localmagic.patch
Patch1: file-4.17-rpm-name.patch
Patch2: file-5.04-volume_key.patch
# Fix close_on_exec multithreaded decompression issue (#1906751)
Patch3: file-5.39-CLOEXEC.patch
URL: http://www.darwinsys.com/file/
Requires: file-libs = %{version}-%{release}
BuildRequires: zlib-devel
@ -205,6 +208,9 @@ cd %{py3dir}
%endif
%changelog
* Wed Dec 16 2020 Vincent Mihalkovic <vmihalko@redhat.com> - 5.39-4
- Fix close_on_exec multithreaded decompression issue (#1906751)
* Mon Jul 27 2020 Fedora Release Engineering <releng@fedoraproject.org> - 5.39-3
- Rebuilt for https://fedoraproject.org/wiki/Fedora_33_Mass_Rebuild