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Do not automatically enable the linux kernel's BPF JIT compiler 

The default value of kernel.unprivileged_bpf_disabled is 0 which means
this is enabling the BPF JIT compiler for unprivileged users. Given that
this is a known attack vector for Spectre variant 1 (CVE-2017-5753) this
is not a setting that a utility should be tampering with.

Tshark's and dumpcap's help message is changed by Balint Reczey to suggest
enabling BPF manually after considering security-related implications.

Change-Id: I1cc34cbd6e84485eba9dee79a8700aa388354885
Signed-off-by: Balint Reczey <balint.reczey@canonical.com>
Bug: 14313
Reviewed-on: https://code.wireshark.org/review/25192
Reviewed-by: Balint Reczey <balint@balintreczey.hu>
Petri-Dish: Balint Reczey <balint@balintreczey.hu>
Reviewed-by: João Valverde <j@v6e.pt>
Tested-by: Petri Dish Buildbot
Reviewed-by: Gerald Combs <gerald@wireshark.org>
This commit is contained in:
Jon DeVree 2018-01-08 01:22:53 -05:00 committed by Gerald Combs
parent aaa980e356
commit 51e0d22ec6
2 changed files with 8 additions and 36 deletions
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37
dumpcap.c
View File

@ -150,32 +150,6 @@ static void capture_loop_stop(void);
/** Close a pipe, or socket if \a from_socket is TRUE */
static void cap_pipe_close(int pipe_fd, gboolean from_socket _U_);
#ifdef __linux__
/*
* Enable kernel BPF JIT compiler if available.
* If any calls fail, just drive on - the JIT compiler might not be
* enabled, but filtering will still work, and it's not clear what
* we could do if the calls fail; should we just report the error
* and not continue to capture, should we report it as a warning, or
* what?
*/
static void
enable_kernel_bpf_jit_compiler(void)
{
int fd;
ssize_t written _U_;
static const char file[] = "/proc/sys/net/core/bpf_jit_enable";
fd = ws_open(file, O_WRONLY);
if (fd < 0)
return;
written = ws_write(fd, "1", strlen("1"));
ws_close(fd);
}
#endif
#if !defined (__linux__)
#ifndef HAVE_PCAP_BREAKLOOP
/*
@ -502,9 +476,10 @@ print_usage(FILE *output)
fprintf(output, " -h display this help and exit\n");
fprintf(output, "\n");
#ifdef __linux__
fprintf(output, "WARNING: dumpcap will enable kernel BPF JIT compiler if available.\n");
fprintf(output, "You might want to reset it\n");
fprintf(output, "By doing \"echo 0 > /proc/sys/net/core/bpf_jit_enable\"\n");
fprintf(output, "Dumpcap can benefit from an enabled BPF JIT compiler if available.\n");
fprintf(output, "You might want to enable it by executing:\n");
fprintf(output, " \"echo 1 > /proc/sys/net/core/bpf_jit_enable\"\n");
fprintf(output, "Note that this can make your system less secure!\n");
fprintf(output, "\n");
#endif
fprintf(output, "Example: dumpcap -i eth0 -a duration:60 -w output.pcapng\n");
@ -4663,10 +4638,6 @@ main(int argc, char *argv[])
#endif /* SIGINFO */
#endif /* _WIN32 */
#ifdef __linux__
enable_kernel_bpf_jit_compiler();
#endif
/* ----------------------------------------------------------------- */
/* Privilege and capability handling */
/* Cases: */

7
tshark.c
View File

@ -454,9 +454,10 @@ print_usage(FILE *output)
fprintf(output, " use \"-G help\" for more help\n");
#ifdef __linux__
fprintf(output, "\n");
fprintf(output, "WARNING: dumpcap will enable kernel BPF JIT compiler if available.\n");
fprintf(output, "You might want to reset it\n");
fprintf(output, "By doing \"echo 0 > /proc/sys/net/core/bpf_jit_enable\"\n");
fprintf(output, "Dumpcap can benefit from an enabled BPF JIT compiler if available.\n");
fprintf(output, "You might want to enable it by executing:\n");
fprintf(output, " \"echo 1 > /proc/sys/net/core/bpf_jit_enable\"\n");
fprintf(output, "Note that this can make your system less secure!\n");
#endif
}