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Другие команды, такие как chown и т. Д., Работают, Так что это как-то связано с snap или nextcloud-snap.

Я попробовал следующее:

 #include <stdio.h>
#include <stdlib.h>
#include <unistd.h> /* for fork */
#include <sys/types.h> /* for pid_t */
#include <sys/wait.h> /* for wait */

int main()
{
    setuid(0);
    /*Spawn a child to run the program.*/
    pid_t pid=fork();
    if (pid==0) { /* child process */
        static char *argv[]={"nextcloud.occ","nextcloud.occ files:scan Administrator",NULL};
        execv("/snap/bin/nextcloud.occ",argv);
        exit(127); /* only if execv fails */
    }
    else { /* pid!=0; parent process */
        waitpid(pid,0,0); /* wait for child to exit */
    }
    return 0;
}
 

Я побежал

 gcc -o posttorrent posttorrent.c
sudo chown root posttorrent
sudo chmod ug s posttorrent
 

запуск программы приводит к:

 permanently dropping privs did not work: File exists
 

затем последовательность выполнения программы приводит к:

 debian-transmission@ubuntu:/transmission-data$ strace ./posttorrent
execve("./posttorrent", ["./posttorrent"], 0xffffd2e7a1e0 /* 13 vars */) = 0
faccessat(AT_FDCWD, "/etc/suid-debug", F_OK) = -1 ENOENT (No such file or directory)
brk(NULL)                               = 0xaaaafeb52000
fcntl(0, F_GETFD)                       = 0
fcntl(1, F_GETFD)                       = 0
fcntl(2, F_GETFD)                       = 0
faccessat(AT_FDCWD, "/etc/suid-debug", F_OK) = -1 ENOENT (No such file or directory)
faccessat(AT_FDCWD, "/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=27061, ...}) = 0
mmap(NULL, 27061, PROT_READ, MAP_PRIVATE, 3, 0) = 0xffffaace6000
close(3)                                = 0
openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF211332671350A2"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1441800, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xffffaace4000
mmap(NULL, 1510480, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xffffaab4d000
mprotect(0xffffaaca6000, 61440, PROT_NONE) = 0
mmap(0xffffaacb5000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x158000) = 0xffffaacb5000
mmap(0xffffaacbb000, 11344, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xffffaacbb000
close(3)                                = 0
mprotect(0xffffaacb5000, 12288, PROT_READ) = 0
mprotect(0xaaaad56ed000, 4096, PROT_READ) = 0
mprotect(0xffffaacef000, 4096, PROT_READ) = 0
munmap(0xffffaace6000, 27061)           = 0
setuid(0)                               = -1 EPERM (Operation not permitted)
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0xffffaace4cf0) = 762022
wait4(762022, 2020/12/21 20:27:47.533491 cmd_run.go:994: WARNING: cannot create user data directory: cannot create "/var/lib/transmission-daemon/snap/nextcloud/24943": mkdir /var/lib/transmission-daemon/snap: permission denied
Sorry, home directories outside of /home are not currently supported.
See https://forum.snapcraft.io/t/11209 for details.
NULL, 0, NULL)            = 762022
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=762022, si_uid=112, si_status=1, si_utime=2, si_stime=5} ---
exit_group(0)                           = ?
    exited with 0