Re: [Xen-devel] [BUG] libxl_ctx_free calls close(0)

[Wei Liu <wei.liu2@xxxxxxxxxx>]

CC Ian Jackson

I don't know which version of Xen you're using. Can you check if it
contains the following commit?

commit fa13f7b0c0f3d01741e35d573009503c3bf7b6a6
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Aug 18 14:02:37 2014 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Wed Aug 27 02:30:25 2014 +0100

    tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

    Otherwise, if it is not used, libxl_ctx_free() will close fd 0.

    Reported-by: Alex Bligh <alex@xxxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
    CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

On Thu, Jul 20, 2017 at 08:36:28PM +0300, Victor Kirhenshtein wrote:
> Hello,
> 
> it seems that libxl_ctx_free always calls close(0) for some
> reason, even if libxl never opens file descriptor 0. It sometimes
> closes valid descriptor in application causing random and
> hard to debug I/O errors.
> 
> The following simple program can be used to reproduce this bug:
> 
> #include <stdio.h>
> #include <libxl.h>
> 
> static void LogMessage(struct xentoollog_logger *logger,
>                      xentoollog_level level,
>                      int errnoval /* or -1 */,
>                      const char *context /* eg "xc", "xl", may be 0 */,
>                      const char *format /* without level, context, \n
> */,
>                      va_list al)
> {
> }
> 
> static void LogProgress(struct xentoollog_logger *logger,
>                      const char *context /* see above */,
>                      const char *doing_what /* no \r,\n */,
>                      int percent, unsigned long done, unsigned long
> total)
> {
> }
> 
> static void LogDestroy(struct xentoollog_logger *logger)
> {
> }
> 
> 
> int main(int argc, char *argv[])
> {
>    xentoollog_logger logger;
>    logger.vmessage = LogMessage;
>    logger.progress = LogProgress;
>    logger.destroy = LogDestroy;
> 
>    libxl_ctx *ctx;
>    int rc = libxl_ctx_alloc(&ctx, LIBXL_VERSION, 0, &logger);
>    if (rc != 0)
>    {
>       printf("libxl_ctx_alloc failed (%d)\n", rc);
>       return 1;
>    }
> 
> 
>    libxl_ctx_free(ctx);
>    return 0;
> }
> 
> Strace output for it is following (I omit shared library 
> loading on startup):
> 
> set_tid_address(0x7f787db29a50)         = 17944
> set_robust_list(0x7f787db29a60, 24)     = 0
> rt_sigaction(SIGRTMIN, {0x7f787c4809b0, [], SA_RESTORER|SA_SIGINFO,
> 0x7f787c489890}, NULL, 8) = 0
> rt_sigaction(SIGRT_1, {0x7f787c480a40, [],
> SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x7f787c489890}, NULL, 8) = 0
> rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
> getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY})
> = 0
> brk(0)                                  = 0x156d000
> brk(0x158e000)                          = 0x158e000
> pipe([3, 4])                            = 0
> fcntl(3, F_GETFL)                       = 0 (flags O_RDONLY)
> fcntl(3, F_SETFL, O_RDONLY|O_NONBLOCK)  = 0
> fcntl(4, F_GETFL)                       = 0x1 (flags O_WRONLY)
> fcntl(4, F_SETFL, O_WRONLY|O_NONBLOCK)  = 0
> open("/proc/xen/privcmd", O_RDWR)       = 5
> fcntl(5, F_GETFD)                       = 0
> fcntl(5, F_SETFD, FD_CLOEXEC)           = 0
> stat("/var/run/xenstored/socket", {st_mode=S_IFSOCK|0600, st_size=0,
> ...}) = 0
> socket(PF_LOCAL, SOCK_STREAM, 0)        = 6
> fcntl(6, F_GETFD)                       = 0
> fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
> connect(6, {sa_family=AF_LOCAL, sun_path="/var/run/xenstored/socket"},
> 110) = 0
> close(5)                                = 0
> close(6)                                = 0
> close(3)                                = 0
> close(4)                                = 0
> close(0)                                = 0
> exit_group(0)                           = ?
> +++ exited with 0 +++
> 
> Best regards,
> Victor Kirhenshtein
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> https://lists.xen.org/xen-devel

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel