.png)
musl libc変更できる権限を削除してもuid問題は再現できません。rootsetuid(1000)glibc
パスワード：
#define _GNU_SOURCE
#include <unistd.h>
#include <stdio.h>
int main(void) {
uid_t r, e, s;
getresuid(&r, &e, &s);
printf("%d %d %d\n", r, e, s);
if (setuid(1000) != 0)
puts("setuid(1000) failed");
else
puts("setuid(1000) succeded");
getresuid(&r, &e, &s);
printf("%d %d %d\n", r, e, s);
if (setuid(0) != 0)
puts("setuid(0) failed");
else
puts("setuid(0) succeded");
getresuid(&r, &e, &s);
printf("%d %d %d\n", r, e, s);
return 0;
}
usingを使用してコンパイルし、gcc -o setuidtest setuidtest.cルートとして実行すると、次の出力が生成されます。
0 0 0
setuid(1000) succeded
1000 1000 1000
setuid(0) succeded
0 0 0
私は走っていますボイドLinux4.18_1カーネルバージョン、muslバージョン1.1.20_2、glibcバージョンがあります。2.28_3
この質問はどこから来たのでしょうか？私のカーネル、musl libc、または私のテストコードは間違っていますか？他の人がこの問題を再現できますか？
strace 出力 (musl 権限なし)
$ strace ./setuidtest (unpriviledged)
execve("./setuidtest", ["./setuidtest"], 0x7ffdd15f69e0 /* 24 vars */) = 0
arch_prctl(ARCH_SET_FS, 0x7f538925cb28) = 0
set_tid_address(0x7f538925cb68) = 6299
mprotect(0x7f5389259000, 4096, PROT_READ) = 0
mprotect(0x55e9c5e75000, 4096, PROT_READ) = 0
getresuid([1000], [1000], [1000]) = 0
ioctl(1, TIOCGWINSZ, 0x7ffd2faf3160) = -1 ENOTTY (Not a tty)
writev(1, [{iov_base="1000 1000 1000", iov_len=14}, {iov_base="\n", iov_len=1}], 21000 1000 1000
) = 15
rt_sigprocmask(SIG_BLOCK, ~[RTMIN RT_1 RT_2], [], 8) = 0
rt_sigprocmask(SIG_BLOCK, ~[], NULL, 8) = 0
setuid(1000) = 0
futex(0x7f538925cfd8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
getresuid([1000], [1000], [1000]) = 0
rt_sigprocmask(SIG_BLOCK, ~[RTMIN RT_1 RT_2], [], 8) = 0
rt_sigprocmask(SIG_BLOCK, ~[], NULL, 8) = 0
setuid(0) = -1 EPERM (Operation not permitted)
futex(0x7f538925cfd8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
getresuid([1000], [1000], [1000]) = 0
writev(1, [{iov_base="setuid(1000) succeded\n1000 1000 "..., iov_len=69}, {iov_base=NULL, iov_len=0}], 2setuid(1000) succeded
1000 1000 1000
setuid(0) failed
1000 1000 1000
) = 69
exit_group(0) = ?
+++ exited with 0 +++
strace 出力 (musl を root として使用)
# strace ./setuidtest (as root)
execve("./setuidtest", ["./setuidtest"], 0x7ffe19286eb0 /* 18 vars */) = 0
arch_prctl(ARCH_SET_FS, 0x7f08b2619b28) = 0
set_tid_address(0x7f08b2619b68) = 6409
mprotect(0x7f08b2616000, 4096, PROT_READ) = 0
mprotect(0x561507eb4000, 4096, PROT_READ) = 0
getresuid([0], [0], [0]) = 0
ioctl(1, TIOCGWINSZ, 0x7fffb222bff0) = -1 ENOTTY (Not a tty)
writev(1, [{iov_base="0 0 0", iov_len=5}, {iov_base="\n", iov_len=1}], 20 0 0
) = 6
rt_sigprocmask(SIG_BLOCK, ~[RTMIN RT_1 RT_2], [], 8) = 0
rt_sigprocmask(SIG_BLOCK, ~[], NULL, 8) = 0
setuid(1000) = 0
futex(0x7f08b2619fd8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
getresuid([1000], [1000], [1000]) = 0
rt_sigprocmask(SIG_BLOCK, ~[RTMIN RT_1 RT_2], [], 8) = 0
rt_sigprocmask(SIG_BLOCK, ~[], NULL, 8) = 0
setuid(0) = 0
futex(0x7f08b2619fd8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
getresuid([0], [0], [0]) = 0
writev(1, [{iov_base="setuid(1000) succeded\n1000 1000 "..., iov_len=62}, {iov_base=NULL, iov_len=0}], 2setuid(1000) succeded
1000 1000 1000
setuid(0) succeded
0 0 0
) = 62
exit_group(0) = ?
+++ exited with 0 +++
strace 出力 (glibc 権限なし)
$ strace ./setuidtest
execve("./setuidtest", ["./setuidtest"], 0x7fff673b2c20 /* 14 vars */) = 0
brk(NULL) = 0x558b5fbb1000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64/x86_64", 0x7ffc25da1650) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64", 0x7ffc25da1650) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64", 0x7ffc25da1650) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls", 0x7ffc25da1650) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64/x86_64", 0x7ffc25da1650) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64", 0x7ffc25da1650) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64", 0x7ffc25da1650) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\3604\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=18248368, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fbcd7093000
mmap(NULL, 3921920, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fbcd6ab1000
mprotect(0x7fbcd6c65000, 2097152, PROT_NONE) = 0
mmap(0x7fbcd6e65000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b4000) = 0x7fbcd6e65000
mmap(0x7fbcd6e6b000, 14336, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fbcd6e6b000
close(3) = 0
arch_prctl(ARCH_SET_FS, 0x7fbcd7094500) = 0
mprotect(0x7fbcd6e65000, 16384, PROT_READ) = 0
mprotect(0x558b5f5c0000, 4096, PROT_READ) = 0
mprotect(0x7fbcd7095000, 4096, PROT_READ) = 0
getresuid([1000], [1000], [1000]) = 0
fstat(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
brk(NULL) = 0x558b5fbb1000
brk(0x558b5fbd2000) = 0x558b5fbd2000
setuid(1000) = 0
getresuid([1000], [1000], [1000]) = 0
setuid(0) = -1 EPERM (Operation not permitted)
getresuid([1000], [1000], [1000]) = 0
write(1, "1000 1000 1000\nsetuid(1000) succ"..., 841000 1000 1000
setuid(1000) succeded
1000 1000 1000
setuid(0) failed
1000 1000 1000
) = 84
exit_group(0) = ?
+++ exited with 0 +++
strace 出力 (ルートとしての glibc)
# strace ./setuidtest
execve("./test", ["./test"], 0x7ffc9176d3f0 /* 15 vars */) = 0
brk(NULL) = 0x5653f4910000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64/x86_64", 0x7ffe7d0c9550) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64", 0x7ffe7d0c9550) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64", 0x7ffe7d0c9550) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls", 0x7ffe7d0c9550) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64/x86_64", 0x7ffe7d0c9550) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64", 0x7ffe7d0c9550) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64", 0x7ffe7d0c9550) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\3604\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=18248368, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb18f5af000
mmap(NULL, 3921920, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fb18efcd000
mprotect(0x7fb18f181000, 2097152, PROT_NONE) = 0
mmap(0x7fb18f381000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b4000) = 0x7fb18f381000
mmap(0x7fb18f387000, 14336, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fb18f387000
close(3) = 0
arch_prctl(ARCH_SET_FS, 0x7fb18f5b0500) = 0
mprotect(0x7fb18f381000, 16384, PROT_READ) = 0
mprotect(0x5653f40df000, 4096, PROT_READ) = 0
mprotect(0x7fb18f5b1000, 4096, PROT_READ) = 0
getresuid([0], [0], [0]) = 0
fstat(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
brk(NULL) = 0x5653f4910000
brk(0x5653f4931000) = 0x5653f4931000
setuid(1000) = 0
getresuid([1000], [1000], [1000]) = 0
setuid(0) = -1 EPERM (Operation not permitted)
getresuid([1000], [1000], [1000]) = 0
write(1, "0 0 0\nsetuid(1000) succeded\n1000"..., 750 0 0
setuid(1000) succeded
1000 1000 1000
setuid(0) failed
1000 1000 1000
) = 75
exit_group(0) = ?
+++ exited with 0 +++
答え1
問題は、実際にはカーネルやmuslで発生するのではなく、機能で発生します。私の2つのテストシステムの間に違いがあることがわかりました。glibcこれmuslは両方のシステムに関連しているようです。
この問題は実際には次のために発生します。pam_rundir.so基準寸法SECBIT_NO_SETUID_FIXUPカーネルが後でプログラムの機能を維持できるようにするセキュリティビットを設定しますsetuid（したがって、をsetuid返すことができますroot）。