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Don't perform fchmodat on symlinks if told not to follow symlinks
In macOS (and some BSDs), symlinks have modifiable permissions, but in Linux, they do not.
Telling Linux to perform fchmodat on a symlink will cause it to modify the permissions on the symlink's target
(and return ENOENT if you try to modify permissions on a symlink that doesn't have a valid target)
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+47
-1
src/kernel/emulation/linux/unistd/fchmodat.c
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-1
src/kernel/emulation/linux/unistd/fchmodat.c
···
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#include "../vchroot_expand.h"
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#include <mach/lkm.h>
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#include <lkm/api.h>
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#include <stdio.h>
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#include "../stat/common.h"
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#include <sys/stat.h>
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extern char* strcpy(char* dst, const char* src);
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extern long close_internal(int fd);
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#ifndef LINUX_O_PATH
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#define LINUX_O_PATH 0x200000
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#endif
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#ifndef LINUX_O_NOFOLLOW
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#define LINUX_O_NOFOLLOW 0x0100
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#endif
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#ifndef LINUX_O_CLOEXEC
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#define LINUX_O_CLOEXEC 0x1000000
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#endif
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#ifndef LINUX_AT_EMPTY_PATH
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#define LINUX_AT_EMPTY_PATH 0x1000
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#endif
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#ifndef __NR_fstatat64
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#define __NR_fstatat64 __NR_newfstatat
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#endif
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int do_linux_fchmodat(int fd, const char* path, int mode, int flag) {
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if (flag == 0) {
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return LINUX_SYSCALL(__NR_fchmodat, fd, path, mode);
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} else {
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struct linux_stat st;
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if (LINUX_SYSCALL(__NR_fstatat64, fd, path, &st, LINUX_AT_EMPTY_PATH | LINUX_AT_SYMLINK_NOFOLLOW) != 0)
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return -1;
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// on Linux, symlinks can't be chmodded (only their targets)
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//
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// we can't open a file handle directly on the symlink
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// and do fchmod/chmod on that because Linux ignores us
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// and follows the symlink anyways
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//
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// this still happens even if we try to open a file handle to
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// the symlink and modify it through `/proc/self/fd`
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//
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// so instead, just return success
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if (S_ISLNK(st.st_mode))
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return 0;
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return LINUX_SYSCALL(__NR_fchmodat, fd, path, mode);
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}
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};
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long sys_fchmodat(int fd, const char* path, int mode, int flag)
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{
···
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if (ret < 0)
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return errno_linux_to_bsd(ret);
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ret = LINUX_SYSCALL(__NR_fchmodat, vc.dfd, vc.path, mode, atflags_bsd_to_linux(flag));
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ret = do_linux_fchmodat(vc.dfd, vc.path, mode, atflags_bsd_to_linux(flag));
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if (ret < 0)
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ret = errno_linux_to_bsd(ret);
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+2
-1
src/kernel/emulation/linux/xattr/setattrlist_generic.c
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-1
src/kernel/emulation/linux/xattr/setattrlist_generic.c
···
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#include <stddef.h>
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extern char *strcpy(char *dest, const char *src);
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extern int do_linux_fchmodat(int fd, const char* path, int mode, int flag);
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#define ATTR_BIT_MAP_COUNT 5
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···
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{
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int perms = *((int*) next);
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#if HAS_PATH
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rv = LINUX_SYSCALL(__NR_chmod, vc.path, perms);
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rv = do_linux_fchmodat(LINUX_AT_FDCWD, vc.path, perms, LINUX_AT_SYMLINK_NOFOLLOW);
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#else
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rv = LINUX_SYSCALL(__NR_fchmod, fd, perms);
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#endif