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Forward Linux capabilities to child process #22

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Forward Linux capabilities to child process #22

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110 changes: 110 additions & 0 deletions src/runtime/runtime.c
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,16 @@ extern int sqfs_opt_proc(void* data, const char* arg, int key, struct fuse_args*
#include <libgen.h>
#include <dirent.h>
#include <ctype.h>
#include <sys/syscall.h>

#if defined(SYS_capget) && defined(SYS_capset)
#define USE_CAPABILITIES
#endif

#ifdef USE_CAPABILITIES
#include <sys/prctl.h>
#include <linux/capability.h>
#endif

const char* fusermountPath = NULL;

Expand Down Expand Up @@ -1459,6 +1469,97 @@ void set_portable_home_and_config(char* basepath) {
}
}

#ifdef USE_CAPABILITIES
int appimage_adjust_capabilities()
{
struct __user_cap_header_struct hdr;
struct __user_cap_data_struct data[_LINUX_CAPABILITY_U32S_3];
int res, datacnt;

hdr.version = 0;
hdr.pid = 0;
res = syscall(SYS_capget, &hdr, NULL);
if (res)
{
if (errno != EINVAL || hdr.version == 0)
{
fprintf(stderr, "SYS_capget syscall failed with %d\n", errno);
return -1;
}
}
else if (hdr.version == 0)
{
fprintf(stderr, "Failed to query capability version\n");
return -1;
}

//fprintf(stderr, "Linux capability version: %x\n", hdr.version);

switch (hdr.version)
{
case _LINUX_CAPABILITY_VERSION_1:
datacnt = _LINUX_CAPABILITY_U32S_1;
break;
case _LINUX_CAPABILITY_VERSION_2:
datacnt = _LINUX_CAPABILITY_U32S_2;
break;
case _LINUX_CAPABILITY_VERSION_3:
datacnt = _LINUX_CAPABILITY_U32S_3;
break;
default:
fprintf(stderr, "Unknown Linux capability version: %x; forcing version 3\n", hdr.version);
datacnt = _LINUX_CAPABILITY_U32S_3;
hdr.version = _LINUX_CAPABILITY_VERSION_3;
}

res = syscall(SYS_capget, &hdr, &data);
if (res)
{
fprintf(stderr, "Failed to query capabilities; error: %d\n", errno);
return -1;
}

//for (int i = 0; i < datacnt; ++i)
//{
// fprintf(stderr, "Set %d: eff = %08x, perm = %08x, inh = %08x\n", i, data[i].effective, data[i].permitted, data[i].inheritable);
//}

for (int i = 0; i < datacnt; ++i)
{
data[i].inheritable |= data[i].permitted;
}

res = syscall(SYS_capset, &hdr, &data);
if (res)
{
fprintf(stderr, "Failed to set capabilities; error: %d\n", errno);
return -1;
}

/* now we can set up the ambient set */
for (int i = 0; i < datacnt; ++i)
{
for (int j = 0; j < 32; ++j)
{
int capval = i * 32 + j;
int capbit = 1 << j;

if ((data[i].permitted & capbit) && (data[i].inheritable & capbit))
{
res = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, capval, 0, 0);
if (res)
{
fprintf(stderr, "Failed to set ambient capability %d; error: %d\n", capval, errno);
return -1;
}
}
}
}

return 0;
}
#endif

int main(int argc, char* argv[]) {
const bool verbose = (getenv("VERBOSE") != NULL);
if (verbose) {
Expand Down Expand Up @@ -1832,6 +1933,15 @@ int main(int argc, char* argv[]) {

set_portable_home_and_config(fullpath);

#ifdef USE_CAPABILITIES
/* Ensure that capabilities for the AppImage are applied to the children (Note: we won't consider
this failing as an error as the application might still work for the usecase intended by the user) */
if (appimage_adjust_capabilities())
{
fprintf(stderr, "Warning: failed to forward capabilities\n");
}
#endif

/* Original working directory */
char cwd[1024];
if (getcwd(cwd, sizeof(cwd)) != NULL) {
Expand Down