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f23513e8d9
The problem is as follows: in multi-threaded code (or more correctly: all code using clone() with CLONE_FILES) we have a race when exec'ing. thread #1 thread #2 fd=open() fork + exec fcntl(fd,F_SETFD,FD_CLOEXEC) In some applications this can happen frequently. Take a web browser. One thread opens a file and another thread starts, say, an external PDF viewer. The result can even be a security issue if that open file descriptor refers to a sensitive file and the external program can somehow be tricked into using that descriptor. Just adding O_CLOEXEC support to open() doesn't solve the whole set of problems. There are other ways to create file descriptors (socket, epoll_create, Unix domain socket transfer, etc). These can and should be addressed separately though. open() is such an easy case that it makes not much sense putting the fix off. The test program: #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <unistd.h> #ifndef O_CLOEXEC # define O_CLOEXEC 02000000 #endif int main (int argc, char *argv[]) { int fd; if (argc > 1) { fd = atol (argv[1]); printf ("child: fd = %d\n", fd); if (fcntl (fd, F_GETFD) == 0 || errno != EBADF) { puts ("file descriptor valid in child"); return 1; } return 0; } fd = open ("/proc/self/exe", O_RDONLY | O_CLOEXEC); printf ("in parent: new fd = %d\n", fd); char buf[20]; snprintf (buf, sizeof (buf), "%d", fd); execl ("/proc/self/exe", argv[0], buf, NULL); puts ("execl failed"); return 1; } [kyle@parisc-linux.org: parisc fix] Signed-off-by: Ulrich Drepper <drepper@redhat.com> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Davide Libenzi <davidel@xmailserver.org> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Cc: Chris Zankel <chris@zankel.net> Signed-off-by: Kyle McMartin <kyle@parisc-linux.org> Acked-by: David S. Miller <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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| .. | ||
| bitops | ||
| 4level-fixup.h | ||
| atomic.h | ||
| audit_change_attr.h | ||
| audit_dir_write.h | ||
| audit_read.h | ||
| audit_signal.h | ||
| audit_write.h | ||
| bitops.h | ||
| bug.h | ||
| cputime.h | ||
| device.h | ||
| div64.h | ||
| dma-mapping-broken.h | ||
| dma-mapping.h | ||
| emergency-restart.h | ||
| errno-base.h | ||
| errno.h | ||
| fcntl.h | ||
| futex.h | ||
| gpio.h | ||
| ide_iops.h | ||
| ioctl.h | ||
| iomap.h | ||
| ipc.h | ||
| irq_regs.h | ||
| Kbuild | ||
| Kbuild.asm | ||
| kdebug.h | ||
| libata-portmap.h | ||
| local.h | ||
| memory_model.h | ||
| mm_hooks.h | ||
| mman.h | ||
| mutex-dec.h | ||
| mutex-null.h | ||
| mutex-xchg.h | ||
| page.h | ||
| pci-dma-compat.h | ||
| pci.h | ||
| percpu.h | ||
| pgtable-nopmd.h | ||
| pgtable-nopud.h | ||
| pgtable.h | ||
| poll.h | ||
| resource.h | ||
| rtc.h | ||
| sections.h | ||
| siginfo.h | ||
| signal.h | ||
| statfs.h | ||
| termios.h | ||
| tlb.h | ||
| topology.h | ||
| uaccess.h | ||
| unaligned.h | ||
| vmlinux.lds.h | ||
| xor.h | ||